Quetico Geology 9781487582616

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QUETICO GEOLOGY

AEHIAL \'JE\Y OF HEBECCA FALLS, QUETICO PHOYI:\"CI.-\L PARK

(Unit eel States Forest Service)

QUETICO GEOLOGY

ByV.B.Mee11 ♦♦♦♦

PUBLISHED FOR THE QUETICO FOUNDATION BY UNIVERSITY OF TORONTO PBF.SS

1959

Copyright, Canada, 1959 University of Toronto Press Reprinted 1973 Printed in Canada Reprinted in 2018 ISBN 978-1-4875-8731-4 (paper) Quetico Foundation Series

1. 2. 3. 4.

By E. S. Coatsworth ByV. B. Meen CANOE TRAILS TIIROUGH QUETICO. By Keith Denis

TIIE INDIANS OF QUETICO. QUETICOGEOLOGY.

INDIAN ROCK PAINTINGS OF THE GREAT LAKES.

By Selwyn Dewdney and Kenneth E. Kidd

Foreword

west of Lake Superior and abutting on the United States-Canadian border, lies the Quetico Provincial Park. Unknown to most of our countrymen, the Quetico is a vast unspoiled wilderness, a kaleidoscope of Precambrian rocks and virgin forests interfaced by a galaxy of lakes and streams, rich in history of Indians and voyageurs and a mecca for those who seek the joy of temporarily living close to nature. Collaborating with the Ontario Department of Lands and Forests to preserve the Quetico and to make it better known and better used, The Quetico Foundation is sponsoring a series of monographs dealing with various aspects of the Park. Quetico Geology, the second of the series, was prepared by Dr. V. B. Meen, Head, Division of Earth Sciences, Royal Ontario Museum; the excellent illustrations are by Mr. Harold Vanstone. Books of this kind should be an inspiration to all to explore the beauties of Quetico-to learn more of the natural history of our great country. During three decades as a mining engineer I have had the good fortune of experiencing the unceasing thrill of life close to nature in Canada's hinterland. For IN NORTHWESTERN ONTARIO,

y·

more than twenty years I have been associated with the development of mines on the very fringe of Quetico Park, so I have come to know it well. Thus, I can attest with some authority to the unsurpassed attractions which Quetico offers to thinking people, young and old. These attractions are surely enhanced if one has knowledge of the natural history of the country. A great deal of such knowledge is presented in this illuminating geological treatise by Dr. Meen. M. s. FOTHERINGHAM Vice-Chairman The Quetico Foundation

vi

Preface

THE LURE of a wilderness region can be likened to spring fever: it plays no favourites in choosing its victims. Quetico Park is an excellent case in point. The mysterious pull of its ancient rocks, its forests, and its sparkling waters is felt alike by business executives and industrial tradesmen, by professional men and whitecollar workers. I am, for example, a geologist, and quite able to attest the truth of this happy state of affairs. My reasons for holidaying in Quetico are precisely those of the fellow vacationers I meet there: to return, for a short while, to the simpler life, a life closer to nature than to the artificialities we have created around us in our modern cities; in a word, to relax. It might seem that a vacation of this sort would prove a busman's holiday for a geologist, since he would be faced with reminders of his regular labours every time he portaged over a rocky ridge or inadvertently steered his canoe onto a submerged shoal. But such, fortunately, has not been the case, and indeed it is because of my professional interest that I feel this little book should be written. Campers who read it, I hope, will be able to appreciate more fully the rocks they meet at every tum-rocks

vii

which, though seemingly mute, nevertheless have a fascinating story to tell. The inspiration to write came to me last summer when I was canoeing through Quetico Park with a friend. Early one evening we found ourselves propped up against the trunks of two great red pines. We were watching the flicker of our campfire's flames, relaxing after the day's travel. Our tent was pitched, our sleeping bags awaited invitingly; but it was still too early to turn in. At first our thoughts turned back to the happenings of the two days that had elapsed since we had left our car at French Lake and withdrawn from the world. Gradually, the hustle and bustle of our normal life had

OUR TENT WAS PITCHED

viii

lessened as we paddled across the lake and negotiated the tortuous bends of French River, slipping out to the smooth surface of Pickerel Lake. Later it lessened even more while, wind-bound on a pleasant point, we dozed in the sun as the great waves pounded against the shore as if reaching out for our frail craft drawn up safely beyond their reach. Later still, the slow trolling for pickerel finally and completely removed any urge to hurry. After a day's portaging and fishing along the Pickerel River, we had become old hands at relaxing. We were now regretting that all our life could not be spent in this way. But we were happy that the wilderness was here for us to enjoy whenever we could find the opportunity. The unchanging wilderness! The same today as it was last year and all the years before; the same as it was when the first fur traders passed this way; the same as it was when the first Indian saw it. We acknowledged the fact, as we lay there, that trees have been burnt, blown down, or died of old age. But nature had replaced them with others and the picture had been maintained. We realized that this is so because the basic elements in our landscape picture-the lakeshore, the river, the rapids, the waterfall-have not changed. That thought repeated itself in my mind and the geologist in me eventually worked its way to the fore. It was a plausible thought, but it was simply not true. I thought of sand grains worn from rocks, piles of rock fragments at the bottom of cliffs, and admitted Ix

that the appearance of rocks may change. I confessed that even the basic parts of the Quetico landscape picture do actually change, but at a rate so slow that my friend and I, even in our relaxed state there by the campfire, could not really appreciate it. Thus, a whole new field of thought was opened up, a realm which I was sure would interest my fellow campers. If the landscape is changing now it must have been changing in the past. What geological changes have taken place here in this spot we know as Quetico Park? Surely it would add to enjoyment if travellers knew something about the changes and processes which have taken place. Hence this small book, presented with my hope that any outdoorsman who reads it will find answers to the questions that must surely cross his mind at one time or another as he surveys the rocks which form the setting of this wilderness region.

X

Contents

FOREWORD

by M. S. Fotheringham

v vii

PREFACE

xiii

ILLUSTRATIONS

In the Beginning

3

The Precambrian Era-Before Life Began

11

Geological Events Following the Precambrian Era 26 Rocks and Minerals to Watch for

32

REFERENCES

47

GLOSSARY

49

ACKNOWLEDGEMENTS

54

xi

lllustratlons Aerial view of Rebecca Falls, Quetico Provincial Park Frontispiece viii Our tent was pitched Our earth must have been a stark place indeed 4 6 Crashing waves against the shore Magma beneath-lava above 7 The Quetico Region ( Q) was covered with water 11 Shale-sandstone-conglomerate 13 Great outburst of volcanic activity 15 Lava flowed over tilted Couchiching sediments 16 The Windigokan sediments were laid on top of the Keewatin lavas 16 The earth's crust was crumpled yet again 17 Magma moved in under these mountain ranges 18 Gritty sandstone became compact quartzite 18 19 Shale became slate Magma flowed through cracks 20 This rock is called pegmatite 22 Once more sedimentary rocks were deposited 23 Another period of igneous activity followed 24 The great glacier moved slowly southward 28 The glacier wore down and rounded the earth's surface 29 xiii

The face of the region was changed They may even exhibit small folds Which way is north? Such breaks are called faults Rugged yet compelling

xiv

30 33 35 42 43

QUETICO GEOLOGY

In the Beginning

the men who study rocks and processes of the earth, believe that some of the world's oldest rocks are to be found in Quetico Park. Presuming this to be so, we should begin our story with the creation of our earth. Just how far back this event was in actual years no one knows with any real degree of precision, but a scientific consideration now places it between three thousand and five thousand million years. Geological evidence points to the fact that the earth was once molten, and many theories have been proposed to account for the origin of the earth leading up to the molten state. The first of these was the Laplacean Hypothesis, which postulated a ball of incandescent gas that cooled and eventually solidified. The modem version of this, called Kuiper's Theory, is that the earth along with the rest of the Solar System grew by the accretion of cold particles which had condensed from clouds of gas in space. As these nuclei became larger they attracted more material, and as they became still larger began to warm up, finally becoming incandescent whirling bodies. As our globe whirled some of its heat was gradually lost in the space which surrounded it and its outer surface cooled down sufficiently to become GEOLOGISTS,

3

solid. Thus our first rocks came into existence. However, these did not provide a permanent shell, for liquid rock and gases continually broke through this crust, spilling out over its surface and forming both new rocks and our first atmosphere. As before, heat was lost to space, and as the steam cooled it condensed to water which poured back down on the hot surface and turned once again into steam. Eventually, this action helped to cool the surface of the earth and some of the rain that fell remained as water, £Hing the hollows and providing our first oceans, lakes, and ponds. At this early stage our earth must have been a stark place indeed. The time was now perhaps three billion

OUR EARTH MUST HAVE BEEN A STAIIX PLACE INDEED

4

years ago; bare rock projected from the sea; no plants or animals existed; liquid rock and fiery gases poured forth from many vents in the surface. Rain teemed down continuously. There was no soil in this early period and consequently the rain ran off the bare rock surface, forming rushing torrents which hastened downward to the seas. As it ran the water picked up loose fragments of rock and carried them along, using them as tools to wear down the beds of streams and cut into their banks. Thus old channels were enlarged and greater streams of water rushed through them, causing the rock to wear away more rapidly. Eventually this period of continuous rain came to an end. The sun shone through the vapours and wanned the surface of the rocks. But, at the daily setting of the sun, the temperature dropped and the rocks cooled. This alternating process brought about a continuing expansion and contraction in the surface rock, and finally it broke away from the colder rock which lay beneath providing more loose material to be carried away into the streams by the water. As one surface was worn away in this manner, a new surface immediately below was exposed, only to suffer the same fate. There were winds in those early days too, and they produced several effects. For instance, they picked up small particles of rock which they dashed against other rocks, helping to erode or wear down the latter. Sometimes these loosened rocks were also carried away by winds and deposited elsewhere, perhaps to fonn sand 5

dunes. Again, the winds lashed the bodies of water, sending crashing waves against the shores. These waves picked up sand grains, and even pebbles, and threw them against the shore, where they continued the process of wearing away the solid rock.

CRASlllNG WAVES AGAINST

THE SHORE

Although the surface of the earth was now cool, the very hot interior continued to cool and, as a result, contracted and tried to draw away from the shell that covered it. The surface was left in an unsupported and unstable position and began to buckle, thereby producing our first mountains. But the actions of the winds and the rains continued as before and in time wore down these elevated rocks, carrying their substance into the valleys and re-levelling the earth's surface. At the same time molten rock, technically known as magma, erupted from below the surface crust and 6

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I ••~-•:.:.•• ( ,.>.!-- ,',1, . ........ 4v•

1

MAGMA BENEATH-LAVA ABOVE

flowed up under the folds which formed these early mountains. Some of the molten rock spilled out onto the surface in the form we know as lava. This lava cooled, solidified, and in time was also worn down. The process of contraction of the earth's interior continued, causing a repetition of the mountain-building process -and, of course, there was a repetition of the process of erosion. Just how many periods of mountain-building followed by periods of erosion there were we do not know. We do know though that rocks in many areas were worked over in these ways many times and the result has been, in some regions, an incomprehensible muddle. However, geologists have managed to unravel at least some of the strands in the mystery and have found certain rocks which appear to be older than any other rocks found nearby, or even older than rocks to be found anywhere else in the world. Some of these truly ancient rocks can be seen in Quetico Park and with 7

these for a starting point, let us make an attempt at tracing the history of this area which is today a wilderness of rugged beauty. We are used to counting time in terms of years, centuries, and even a few millenia, and to dating happenings more or less exactly. However, when dealing with geological happenings, we find that our time divisions are very much larger and that we must consider time in terms of millions of years. The longest division of time the geologist uses is the "era." He does not put a limit of so many hundred million years to an era, but rather lets it include a great event or series of related events, which were of worldwide significance. The next largest division of time, geologically speaking, is the "period." Here again, we have difficulty in placing a beginning and end to such a period, which in itsell may have lasted fifty million years or more. A great advance of the sea over the land and its eventual withdrawal; a prolonged and widespread outburst of volcanic activity; the advance and retreat of an ice age of continental magnitude-these may be called periods. Rocks which were produced during one of these periods are often named after that period, and if these rocks were sediments laid down on top of one another, they are known as a series bearing that period's name. Thus the sediments laid down during the Couchiching Period, when the seas invaded the Quetico Area, are called the Couchiching Series. There was a time when no life existed on our earth, 8

and then when it did appear it must have been very primitive. The organisms were probably single-celled with no hard parts. As time passed, these developed into more complex types of animals and plants. When these various organisms died, they were buried in the sand or mud of the sea floor, where their hard parts were replaced by some mineral such as silica and their form was thus preserved. These fossils, as we call them, tell us of the type of life which flourished at various times, and help us to correlate the rock formations of various parts of the earth and to date them. Actually, the dating was done originally by estimating the length of time that must have elapsed while a certain thickness of sediments was deposited, or while a certain form of life was evolved from an earlier one. This latter type of dating could be done only where fossils were present. In recent years, dating of rocks has been assisted by the discovery that the chemical elements, uranium and thorium, break down into various other elements, of which lead is one, at a regular rate. It is possible, therefore, by determining the amount of lead and uranium or thorium in the rock specimen, to estimate the number of years since that rock was formed. This method is of increasing value to us in unravelling our complicated geological history. As geologists worked backward through history, studying, naming, and correlating the various eras and periods, they came to the oldest in which they found fossils, the Cambrian Period as they called it. In the Cambrian rocks there were great quantities of fossils, 9

indicating prolific life during that time. Yet in the great complex of rocks older than the Cambrian, there was little if any evidence of life. The very nature of these rocks indicated that a vast passage of timeprobably longer by far than that indicated by the fossil-bearing rocks-must have taken place while they were produced, eroded, folded, and metamorphosed. Since all these operations took place before the Cambrian, this time was called the Precambrian Era. The complex of rocks formed in the Precambrian Era and now exposed on the surface of the earth is so vast in area that it covers about half of Canada, and indeed constitutes large areas of the exposed rocks of some other countries. These large areas are called the Precambrian Shield. Let us now consider the Precambrian Era and the principal happenings as indicated by the rocks i:hat have been formed in the several periods into whkh this era is at present divided.

10

The Precambrian EraBefore Life Began THE COUCIIlCIIlNG PERIOD

In those distant times, so remote from us that geologists can just begin to comprehend the passage of events, the Quetico region was covered with water. It was not deeply submerged, for Quetico lay near the shoreline of the ocean which had flowed in over the land. On this shoreline the waves, as we have seen, beat continuously, undercutting and wearing down the cliffs. Fragments of rock fell into the water and were

THE QUETICO REGION (Q) WAS COVERED WITH WATER

11

lashed by the waves. They rolled back and forth, grinding against one another and against the floor of the sea. In time they became smaller and were eventually reduced to grains of sand and particles of mud. When they reached this stage, they were carried further out. Sand and mud were also washed into the sea by the waters of the rivers which wore down their beds and their banks. This sediment, too, was washed out away from the land and joined what had been produced by the actions of the waves. Then, out at sea, where the force of the waves was greatly reduced, the sediment was deposited, first the heavier pebbles, then the grains of sand, and then the mud to produce eventually a thick layer on the sea floor. It is hard to appreciate the length of time it took to build up this layer. Since the depth of the sea varied from time to time, mud would sometimes be laid on sand and sometimes sand would be laid on mud. Quite possibly tens of thousands of years passed while the shores were worn or eroded away and the sediment dropped in these ever thickening deposits out at sea. One interesting result of this process was that the weight of the deposits became so great that it pushed down the floor of the ocean beneath. At the same time the shoreline, lightened by the process of erosion, allowed the forces at work in the earth's crust to push up more rock from beneath-rock which would in tum be subjected to the eroding effects of the water. Now, on the ocean floor, as the gravel, sand, and 12

mud were pressed down deeper and weighted down by the fresh material piled on top, they were squeezed and compressed. As a result, they became solid or consolidated rocks, which, in geologist's terms, are given three distinctive names-conglomerate, sandstone, and shale.

SHALE SANDSTONE CONGLOMERATE

Conglomerate is composed of pebbles, often wellrounded, and boulders of various sizes. The spaces between these fragments are filled with grains of sand. In colour the rock is usually grey but the pebbles may be almost any colour and this, of course, affects the colour of the rock itself. Sandstone is a "layered" rock composed of small grains of sand held together so lightly that it is often possible to pull the grains loose with the fingers. It is 13

usually grey or red in colour ( but may be white) and is quite gritty to the touch. Shale is also a layered rock but is composed of particles of clay and some minerals which are so small that they cannot be distinguished even under a magnifying glass. This rock is soft and smooth to the touch and slippery when wet. It also has an earthy odour when damp or wet. Generally shale is grey in colour but may also be white, red, or of a greenish tinge. It is possible, when clay was mixed with sand, to have a muddy sandstone or, where sand was mixed with the clay, to have a sandy shale. Geologists refer to this period-when this great thickness of sandstone and shale was deposited on the sea floor-as the Couchiching Period. It continued over a long period and the layers which were so deposited are logically known as the Couchiching Series. THE KEEWATIN PERIOD

The period which followed the Couchiching witnessed a great and continued outburst of volcanic activity. All over the world, countless numbers of volcanoes burst into action, spewing ashes and fragments into the air and pouring tremendous volumes of molten rock, or lava, over the surface of the earth. Some of this lava poured out over the dry land and some into the oceans. Ash and cinders rained down from the skies-surely a frightening spectacle, although there were no human beings or even, in all likelihood, living organisms of any kind to witness the scene. 14

GREAT OUTBURST OF VOLCANIC ACTIVITY

The greatest quantity of material which was ejected in this way from the volcanoes was lava, and this solidified into dense and fine-grained rocks called trap or basalt. The lava "flows" were often many yards in thickness and as one particular flow began to solidify another would pour out over it, thus piling flow on top of flow to a considerable depth. The geologist's term for this violent period is Keewatin. As during the preceding Couchiching Period the process of erosion continued, producing sediments as before. But in addition to sediments similar to those of the Couchiching Period there were deposits of a peculiar rock called "iron formation." This was a laminated or thinly layered rock, made up of alternating black bands of an iron mineral, magnetite, and red bands of jasper. During this period there were adjustments in the earth's crust which caused some areas to rise and others 15

to sink. Layered rocks such as the Couchiching sandstones and shales were tilted from their original horizontal positions and buried beneath the Keewatin lavas and sediments.

THE WlNDIGOJCAN SEDIMENTS WERE LAID ON TOP OF THE KEEWATIN LAVAS

LAVA FLOWED OVER TILTED COUCHICHINC SEDIMENTS

THE WINDIGOKAN PERIOD

The volcanic eruptions eventually came to an end. The waves, however, continued to beat against the shorelines of the oceans and new deposits of sediments were laid down on the sea floors. Once again there were deposits of materials which, when consolidated, produced conglomerate, sandstone, shale, and even iron formation. This layer of sediments, which was laid down later than, and on top of, the Keewatin, is 16

known in many parts of Ontario as the Temiskaming Series of rocks. However, in the Quetico region the rocks thought to have been formed at this time are called the Windigokan Series. THE ALGOMAN PERIOD

Following the erosion and deposition which characterized the Windigokan Period there came new activity and movement. Great layers of Couchiching, Keewatin, and Windigokan rocks, which still covered the surfaoo in spite of the continuous erosion, upfolded to produce great mountain ranges, thus crumpling the earth's crust yet again. Tremendous volumes of molten rock, called magma, moved in under these mountain ranges and dissolved vast quantities of the older rocks, thus making more room for the molten rock. It was indeed a time of great

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t" ~lf-,

I

TIIE EARni's CRUST WAS CRUMPLED YET AGAIN

17

MAGMA MOVED IN UNDER THESE MOUNTAIN RANGES

geological readjustment; the tremendous pressures which forced the sedimentary and volcanic rocks into their new positions in the mountain chains squeezed them so hard that they became altered or metamorphosed into entirely new rocks. For instance, sandstone, the grains of which ( mostly quartz) had once been so loosely knit together, was now changed into a compact rock called quartzite with

m••-~ ffl •-~ sandstone

pressure

quartzite

GRITTY SANDSTONE BECAME COMPACT QUARTZITE

18

grains completely interlocked after the fashion of a jig-saw puzzle. In fact the rock might be mistaken for massive quartz, except that its layered nature is still often apparent to the eye. At the same time, the shale became much denser and developed into slate, which splits readily, as we used to see in school black boards. In this transformation the mineral kaolin, which had been responsible for

shgJe

pressure

slgte

SHALE BECAME SLATE

the earthy odour of shale, was completely changed to other minerals and in the process the odour was lost. The muddy sandstones changed too, developing into strange, easily split rocks called schists, in which the flakes of mica are obvious to the eye. The conglomerates, though squeezed, still showed the presence of the pebbles and boulders from which they had been originally composed. The volcanic rocks did not escape change: they too were squeezed and consequently altered. Some became easy to split, a condition geologists call schistose. Many of the dark minerals changed either then or 19

later to a new mineral, called chlorite, which is green. Thus we call these changed rocks greenstone or greenstone schist. There were other forces at work besides pressure producing these changes. The vast quantities of molten rocks pushing up through the sediments and volcanics heated the rocks to temperatures which frequently produced quite marked though local effects upon them. As they were folded the tension which was developed caused the rocks to split. As a result, great earthquakes shook the earth and magma flowed up through the cracks to solidify in bodies which, though thin, might sill

MAGMA FLOWED TIIBOUGH CRACKS

none the less extend for hundreds of yards, or even miles, across the rocks. When such a tabular body cuts across the rocks, it is known as a dike. However, if it lies parallel with the bedding of sediments or volcanic flows, it is called a sill. 20

This great infiltration or intrusion of molten matter continued probably for millions of years, slowly folding the sediments and volcanics, pressing them into new metamorphic rocks, squeezing into them thin sheets of magma which became dikes and sills. The intrusion also implanted tremendous quantities of magma underneath these rocks. Gradually, however, this activity came to an end. Slowly the great masses of magma gave off their heat to the surrounding and overlying rocks, heating them and changing those nearest in a variety of ways. As the bodies of magma cooled, they became solid, and today most of them are light in colour and are known to us as granite. Some of the smaller bodies, however, are darker in colour and are known variously as diorite, gabbro, and peridotite, and by other geological terms, depending upon their mineral composition. In the final stages of the cooling some interesting conditions developed. Thin watery fluids collected which were squeezed into cracks in the surrounding rocks and even into the newly formed granite. 'When these fluids solidified, two types of rock were produced. The first was very coarse-grained, consisting of a combination of glassy and usually colourless quartz and an opaque and often pink mineral known as feldspar. This rock is called pegmatite. The second was composed almost entirely of quartz and is now referred to as a quartz vein. Many rare chemical elements were concentrated in these rocks which were produced by the Huids-ele21

ments such as tin, tungsten, lithium, and gold. They had been deposited there when the fluids we spoke of earlier had solidified and as a matter of fact include

THIS ROCK IS CALLED PEGMATITE

nearly all our gold deposits of today and some of our

copper and other economically useful metals. This great period, a time of mountain-building and of the squeezing of fluids between the layers of rocks, has been called the Algoman Period. It probably lasted millions of years and when it drew to a close all the rocks that had been deposited previously had become deformed and changed in appearance, so much so that some of the granites which were formed early in this period had become squeezed and somewhat banded and streaked in appearance, thus producing what we now call gneiss ( pronounced "nice"). 22

THE ANIMIKIE PERIOD

A period of erosion followed, how long we do not know, but we do know that it was sufficiently long to allow the erosion of vast thicknesses of rocks. In some places so much rock was removed that the great masses of granite lying buried under thousands of feet of the folded Couchiching, Keewatin, and Windigokan rocks were laid bare. Much later still, when these mountain ranges had been worn so that their roots were exposed and their surfaces virtually flattened, the seas returned to the Quetico region. Once more sedimentary rocks were deposited on top of all the older rocks. Some conglomerates were laid down but the most predominant deposits consisted of great thicknesses of iron formations and shaley rocks, and these have become known as the Animikie sediments.

+

+

.

+

+

ONCE MORE SEDIMENTARY ROCKS WERE DEPOSITED

23

+

11IE KEWEENAWAN PERIOD

Another period of igneous activity followed the Animikie Period, when lava poured out over the surface of the rocks and magma was injected into the :fissures in the older rocks to form dikes, or between layers of sedimentary rocks to form sills. The rock of these dikes and sills is coarse-grained and black today, although it turns rusty-brown on exposure. It is called diabase by geologists.

ANOTHER PERIOD OF IGNEOUS ACTIVITY FOLLOWED

The result of this activity was the production of many of our great ore deposits, such as the nickelcopper of the Sudbury district, the silver of the Port Arthur region, and the copper of Isle Royale and Keweenaw Point in Michigan. This period, very important from the modern mining point of view, is called the Keweenawan Period. In some other parts 24

of the world, there has been subsequent mountainbuilding and folding of the Keweenawan and older rocks, but in the Quetico there has been relatively little disturbance of this nature since the deposition of the Animikie sediments and the intrusion of the Keweenawan sills. We can only guess at the length of time which elapsed while these processes we have described took place. However, there seems to be ample evidence to lead to the conclusion that at least a billion and a half ( fifteen hundred million) years went by from the laying down of the first sediments of the Couchiching Series along such spots as the Maligne River to the intrusion of the great diabase sills in Keweenawan time just southeast of the Park at North Lake and extending east in both Ontario and Minnesota to Lake Superior. It is also believed that the Keweenawan Period ended about five hundred million years ago. What sort of climate prevailed in the Quetico during these millions of years? Likely it was similar to that of more recent times. In the Windigokan Period, for instance, glaciers moved across the region carving the landscape and depositing materials. Later, climatic conditions went to the opposite extreme and produced arid desert conditions. We are also tempted to enquire whether or not life existed during these early periods. There is some evidence that it did, but either it was not abundant or else the organisms which existed did not have hard parts to leave behind for posterity when they died. 25

Geological Events Following the Precambrian Era THERE are no consolidated rocks in Quetico of an age younger than those of the Precambrian Era. This of course does not mean necessarily that the seas never advanced again over this area. However, if they did, any rocks deposited in them have since been completely removed. During the five hundred million years which we think has elapsed since the end of the Precambrian Era, the Quetico area has stood above the sea probably most of the time, and therefore was exposed to the actions of many erosive agents. For example, even the alternating heat of day and cold of night has helped over the centuries to break up the surface rocks and expose new surfaces below. Again, chemicals picked up by rainwater from the atmosphere or from decaying vegetation attacked the minerals in the rocks, loosening particles which could be picked up and carried away either by wind or water. In arid times the wind becomes a major agent of erosion, picking up small particles and hurling them against other rocks, thus helping to wear down both. Climates change from one extreme to another and back again over the years, as can be seen clearly in the State of Arizona, where today the only remaining evidences

26

of the great trees and sweeping rivers of ancient times are their remains in the petrified "forest" and dried-up channels. In times of abnormal and even normal rainfall, the rivers which carry the rainwater to the sea carry a great deal of sediment. The faster a river flows, in fact, the more sediment it is capable of carrying. Such a "load" acts in much the same manner as does the grit on sandpaper, for it wears down river bottoms and cuts back the banks. On lake shores the pounding of the waves batters the rocks and breaks them up, thus adding to the sediment which may be carried away. Eventually many of these fragments accumulate along the shorelines and in time perhaps become new beds of conglomerate, sandstone, or shale. On more than one occasion during geological time the climate of the Quetico region has changed considerably. The average annual temperature has gone down and brought about glacial conditions. This is not to say that the temperature dropped greatly, as will be seen when it is realized that if the average daily temperature is lowered merely by a degree or two, the snows of winter will come earlier in the autumn and remain later in the spring. If this lowering of the temperature continues it will not be long before the snow-free period of summer will disappear completely. As the years pass, the snow on the ground will become deeper and deeper and the resulting pressure from above will cause the snow below and nearest to the surface of the ground to tum to ice. As the weight from 27

above continues to increase, the ice will begin to move outward over the surrounding territory in the form of a sheet of ice, called a glacier. Such a condition developed north of Quetico about one million years ago and the great glacier thus created moved slowly but surely outward. Part of it travelled southward over what is now the Park, an awesome spectacle, probably several thousands of feet thick. As it moved, it pushed loose rock fragments ahead of it or carried them beneath it. Many of these pieces were of tremendous size and acted as files and chisels as they moved, scoring and scouring the surface of the earth as the glacier passed by.

THE GREAT GLACIER MOVED SLOWLY SOUTHWARD

28

THE GLACmR WORE DOWN AND ROUNDED THE EARTii'S SURFACE

We do not know what thickness of bedrock was removed in this way. However, we do know that all the soil that had been produced through countless millions of years of exposure of the rock to weathering processes was removed, thus exposing tremendous areas of bare unaltered bedrock, not only in Quetico but throughout the Precambrian Shield, to view. Certainly considerable thickness of bedrock was worn away, and the surface which remained was rounded off. Indeed, much of it was highly polished by this action, although in many cases it was also scratched, as we can see plainly today. In time the average annual temperature rose again. The great glacier melted, leaving as a sort of protective covering the load of debris which it had carried or pushed over much of the land it had traversed. The face of the region was changed considerably: old river channels were now filled in or destroyed; new 29

THE FACE OF THE REGION WAS CHANGED

basins were hollowed out or fashioned by the irregular depositions of the debris, which geologists call glacial moraine, and the basins filled up with water left by the melting ice. That is why there are so many lakes in Quetico, and in fact throughout the Precambrian Shield. Since there were no rivers left as such, the water simply spilled over from one basin to another. Little by little these spillings created new rivers, and once again the whole cycle of erosion was begun. As the glaciers retreated, vegetation much like that of today became established. Low-lying areas became marshes and bogs, and the forest matured on the drier 30

ground. Animals, the immediate ancestors of the present fauna, took up their residence in the Quetico habitat. Looking back from the middle of the twentieth century, we know that only a few thousand years, the merest tick of the clock of geological time, separate us from the time when the glacial ice finally melted in Quetico Park. But we must remember that the rocks and minerals of this magnificent region are the results of many geological processes which have taken place with infinite slowness over a total period of probably three thousand million years and are still talcing place in the same slow manner.

ii

Rocks and Mlnerals to Watch For

to be seen today in Quetico Park belong to the Couchiching Series. They are possibly a billion and a hall to two billion years old. At one time they covered the entire area of the Park but they have since been so folded and eroded that they now present but a single arm of a recumbent "U," the bottom of which lies just outside the Park to the west ( see endpaper map). The upper arm of the "U" stretches across the area to the north, by the Canadian National Railway and Highway 120. The band of sediments which lies within the Park is fourteen miles wide between Quetico Lake and Lac La Croix but it narrows to a width of less than hall a mile where it crosses Heronshaw Lake and northwest of Kawnipi Lake. It does widen again however near Cache Lake, but it narrows once again to approximately one mile in width when it crosses the railway track west of Kashabowie. At one time the rocks in these bands were sandstone, shales, and mixtures of the two. During the intense folding-aided locally by heat from the invading masses of granite magma-they changed to banded and cleavable gneisses, mica schists, slates, and impure quartzites. The bands and layers of these rocks are occasion-

THE OLDEST ROCKS

32

ally horizontal but are more often inclined at a considerable angle. They may even exhibit small folds. One that attracts considerable attention is on the south shore of the west end of Fem Lake on the Pickerel River.

TIIEY MAY EVEN EXHIBIT SMALL FOLDS

These gneisses, schists, slates, and quartzites are predominantly grey in colour, often with a little rustiness showing along the planes where they split. On closer examination it is obvious that the four rocks named above encompass an amazing variety of rocks, owing to the variations in the proportions of sand and mud in the original rocks and the local differences in stresses and heat applied to them. For example, several varieties may be seen around the Twin Falls at the head of Bell Island in the Maligne River. One of these has a strange, wart-like appearance due to the development of crystals of cordierite, a mineral which was not 33

in the original muddy sand but which was formed by the heat and pressure. Actually narrow bands of these sediments occur in many parts of the Park and in the area nearby, for instance along Highway 120, and are easily recognized by the characteristics we have just described. The next oldest rocks in Quetico are the volcanics and the sediments of the Keewatin Period. These, like the Couchiching rocks, have been changed or metamorphosed by the folding and heat to which they were subjected in ages past. As a result, they are now greenish in colour and somewhat cleavable. They are usually called greenstone or greenstone schist. In a few places, the changes just described produced small deposits of talc. These Keewatin lavas and associated rocks once covered the whole area and in fact it is quite probable that they covered the whole country at one time. But, as with the Couchiching sediments, so much erosion has taken place since they were deposited that today there is relatively little left of them to see. Within the Park proper, the only rocks of this age visible are located along the southeast border forming the very abrupt shorelines of That Man, This Man, Other Man, Saganagons, and Saganaga lakes. The interesting rock known as iron formation can be seen in outcroppings along the shores of Sheridan, That Man, This Man, and Other Man lakes, as well as in the string of lakes to the south known as Carp, Emerald, and Plough lakes. This iron formation is made 34

up of alternate bands of hematite, jasper, and white quartz, or in some cases of magnetite, jasper, and white quartz. In either case, it is very striking in appearance and easy to spot where it appears as outcroppings along the shores of the lakes. In most cases, the bands are standing up vertically. There is just such a striking outcropping on the point near the southwest end of Emerald Lake. Here the iron formation consists of hematite and broad bands of jasper, which in this particular case is very beautiful. Iron formation of an unusually crumpled nature occurs on the west shore of Cypress ( or Otter Track) Lake. The magnetite in

WlllCB WAY IS NORTII?

these various iron formation bands may cause considerable attraction or deviation to the compass needle and thereby be troublesome to an unwary traveller. Rocks of the Temiskaming or Windigokan Period 35

are seen only in the southeast corner of Quetico Park, although rocks which look similar occur farther north along with the Keewatin Period rocks on the shores of Steep Rock Lake, where they are logically called the "Steep Rocks Series." They consist mostly of beds of conglomerate which contain pebbles and even large boulders of granite and other rocks, as well as pure quartzite and slate. In many instances, they are quite similar in appearance to the rocks of the Couchiching Series and may be confused with them. However, where they occur on the shores of the west bay of Cache Bay on Saganaga Lake, granite boulders the size of footballs firmly fixed in the grey rock call attention to these occurrences and make identification easy. The rocks of the Couchiching, Keewatin, and Windigokan periods were steeply folded in Algoman time and invaded by tremendous masses of magma which cooled and solidified at depths of many thousands of feet below the surface. Since then, erosion has removed much of the older overlying rock and has even eroded much of the intruded Algoman rock as well. The folding we have talked about took place on so grand a scale that we are unable to see the folds. They are much too great in size. We can recognize that it happened, however, because we find sedimentary and volcanic rocks, which were originally laid down flat, in inclined positions. On the other hand, we are able to recognize the folding when it is visible on a smaller scale. Small folds in iron formation are common, for instance, and may be seen in many places in the south36

east corner of the Park. In fact, as mentioned above, a fold of modest size is visible on the western shore of Cypress ( or Otter Track, on some maps) Lake where beds of iron formation form a large arch. Again, a very interesting small fold occurs in the Couchiching sediments on the south banks of the Pickerel River as it leaves Fern Lake. Most of the rock exposed in the Park and in the general vicinity is granite of the Algoman Period. Some of the granite is pink, some is grey, and sometimes it is banded, or gneissic. Generally this rock is coarse in texture with the grains of the various minerals being all approximately the same size. However, a peculiar variety occurs around Saganaga Lake, in which the grains of quartz are unusually large, sometimes as much as half an inch across. There were other kinds of rocks intruded in Algoman time but these were usually in small bodies and their total volume was not great. One of the most interesting is a coarse black rock, known as peridotite. Some of these bodies have been changed by chemical alteration into serpentine and talc. The largest body of this type in the Park occurs on the northeast shore of Cache Bay, at the southwest end of Saganaga Lake. It is now mostly serpentine though it contains a few stringers of asbestos and fibrous brucite, which is known as nemalite. The older rocks of the area would have had no economic significance of their own had it not been for the mineralization which came with the invading granite. Fluids carrying small quantities of gold were 37

squeezed into cracks in these older rocks and produced quartz veins containing varying amounts of gold. A number of these veins have been investigated in the greenstone areas immediately east of the Park, particularly near Shebandowan Lake. Minerals of a number of other economically useful metals were also deposited at about this time. Most of the discoveries made so far of these minerals are in the Keewatin greenstone, to be found north of the Canadian National Railway and in the greenstone area to the east around Burchell and Shebandowan lakes. These metals include copper, chromium, lead, and nickel. The granite intrusion was also responsible for the formation of dikes of pegmatite. Usually they consist predominantly of quartz and feldspar in very large grains and many may be seen along the shores of Pickerel Lake. Sometimes they contain other minerals in varying amounts. Such a one is the pegmatite dike on the Maligne River, immediately upstream from the Twin Falls at Bell Island. It can be seen on the north bank and stretches for a considerable distance. In this dike there are numerous greenish crystals, sometimes several inches in length, of the mineral known as spodumene. This is a source of lithium which is used in the ceramic industry, in the production of the red colour in fireworks, and in special fuels. Outside the Park, there is also a pegmatite dike on an island in Turtle Lake about twenty miles northwest of Atikokan. Geologists have found translucent beryl 38

crystals up to two inches in length and of a yellowgreen colour in this dike. Transparent blue beryl is the gem aquamarine and the green variety is the valuable emerald. Unfortunately for fortune seekers, no crystals of gem quality have been observed in this dike. Molybdenite, the ore mineral of molybdenum, is found in the pegmatite dikes on an island in the west end of Crowrock Lake, to the east of Turtle Lake, also a few miles north of the Park. It has also been seen in other pegmatite dikes in the vicinity. In spite of the variety of minerals of economic value which are to be found in and near Quetico Park, only two have so far been proven to be present in quantities which are economically feasible to extract. These are the iron ore of Steep Rock Lake and the copper deposit of the Coldstream Mine on Burchell Lake. The origin of the iron ore has been-and still is-the subject of a great deal of research. However, geologists of Steep Rock Iron Mines are now of the opinion that the ore was deposited in the Windigokan or Temiskaming Period and enriched and metamorphosed in a small way by magmatic solution accompanying igneous rocks in the Algoman Period. The ore found here is goethite, the brown iron oxide, and, in smaller quantities, hematite, the red iron oxide. When this ore is mined, miners and machinery-everything which comes into contact with it-becomes coated with red mud. As a result the entire area has now taken on a reddish hue. There has been very little deformation in this part of 39

the world since the Animikian sediments were deposited. Hence these appear quite fresh, unchanged or unmetamorphosed, and lie almost flat on top of the older rocks. There are no rocks of this period within the Park limits but a considerable area of them lies exposed to the east, extending from Gunflint on the International Boundary east to Port Arthur. This series of rocks is composed of a thin bed of conglomerate overlain by iron formation and shaley sediments to a depth of almost two thousand feet. The highly silicous iron formation which occurs in the Animikie may some day possibly be mined as a source of iron. The Keweenawan diabase occurs as tabular bodies or sills between the strata of the Animikie. The rock is coarse-grained and nearly black where its surfaces are fresh although this soon turns a chocolate brown when exposed to the weather. There are none of these sills in Quetico Park but they may be seen at Gunflint Lake and eastward. When this diabase was put in place numerous occurrences of calcite veins containing silver were introduced into the surrounding rocks. The famous silver deposits of Silver Islet, east of Port Arthur, and Silver Mountain to the west were formed at this time, as were the native copper deposits on Isle Royale and Keweenaw Peninsula in Michigan. The great ice sheet which moved across so much of the surface of Canada during the past million years eroded and removed great quantities of the rock formations, as we have seen. It was also responsible for much 40

of the present topography of the country. The multitude of rocky, hummocky hills and small, irregularly shaped lakes which dot the region are the direct results of the action of the ice, which scoured the surface and then deposited a mantle of boulders, sand, and clay over much of the area which in turn had the effect of blocking up the existing drainage system. But as we have seen a new system of drainage worked itself out, a system of lakes which are linked by small streams and separated by ridges of bare rock or by patches of swamp-a system which provides many of the attractions of the wilderness. There are a number of places where we can see scratches on the rocks which indicate the route of the great glacier. The best places to look are along the lakeshores where bare, solid rock is exposed between the water and the mantle of boulders and sand left behind by the ice. A few of the places where you may see such scratches or glacial striae are the shore of Sturgeon Lake west of Sturgeon Narrows, the shores of Knife Lake, Cypress ( Otter Track) Lake, and Saganagons Lake, and the west shore of Cairn Lake. At times in the past there were great ruptures in the earth's crust, accompanied by terrible earthquakes and by movement of the rocks along the broken surfaces. Such breaks in the earth's crust are called faults and there are many to be seen in Quetico. They can be observed readily in the Animikie and Keweenawan rocks, for example, which are relatively young and unchanged. In all probability the channel of the river 41

SUCH BREAKS ARE CALLED FAULTS

which flows out of Cache Bay and into Saganagons Lake over the spectacular Silver Falls lies in a fault which broke across the greenstone rocks at this point. The cliffs along the river shore give good indication of this. Then, the long straight west shore of Agnes Lake, with its great cliffs, and the occurrence in a straight line of Kahshapiwi, Keefer, Sark, and Cairn lakes-and even beyond-a total distance of over fifteen miles, provide two illustrations of positions where great faults have occurred in the distant past. Possibly we may never learn how much movement there was along these faults, but the earthquakes which accompanied these adjustments of the tensions and pressures in the earth's crust here would have inspired great fear had any observer been unfortunate enough to have witnessed them.

Rapids and waterfalls provide some of the most picturesque portions of a canoe trip and they are indications of geological processes which are still in progress, so to speak. In such places we can see the rushing water endeavouring to cut into the river bed, dashing aside 42

the obstructions in order to provide a continuous and uninterrupted waterway across the country. Wonderful examples may be seen at the Twin Falls on the Maligne River, Silver Falls out of Cache Bay on Saganaga Lake, Chatterton Falls, Rebecca Falls, and others too numerous to mention but most fascinating to watch. As time passes, these hurrying, tumbling waters will wear away the beautiful but ( to the water) bothersome obstructions, cut back through the lake waters above them, and so reduce the waterways of Quetico Park to a monotonous series of streams flowing at a very gentle rate-without falls or rapids and consequently without portages. However, this state of affairs will not come about for many years, indeed, for many thousands of years to come. At the same time that these processes of erosion are at work cutting down the rocky surfaces there will be other processes at work impeding their progress. There

RUGGED YET COMPELLING

43

is no reason why glaciation-the work of a glacier-or even mountain-building accompanied by further vulcanism cannot begin again. We can only be thankful, in the middle of the twentieth century A.D., for the many geological processes which have provided for us the present topography of Quetico Park and the surrounding region, a land of multitudinous lakes, streams, rapids, and waterfalls, a land formed of an infinite variety of rocks and minerals which give the shorelines their varied appearance. In a word, let us be grateful for the wilderness, a rugged yet compelling region, attractive and hospitable to those who come to study and learn its secrets and thereby increase their own personal enjoyment.

44

REFERENCES AND GLOSSARY

References

the foregoing pages dealing in a very generalized way with the geological happenings in the Quetico Park have aroused an interest in the reader to delve deeper into the subjects of geology and mineralogy, reference may be made to one or more of the following books or maps. IF

GEOLOGICAL MAPS

"Quetico." Dept. of Mines & Resources, Canada. Maps 432A and 534A, 1938. Scale 1 inch equals 4 miles. "Kenora Sheet." Dept. of Mines & Resources, Canada. Map 266A, 1939. Scale 1 inch equals 8 miles. BOOKS

Canoe Trails through Quetico by Keith Denis (Quetico Foundation Series no. 3; distributed by University of Toronto Press Book Department). Elements of Geology by James H. Zumberge (John Wiley and Sons). Geology and Man by Kenneth K. Landes and Russell C. Hussey (Prentice-Hall) . Geology and Economic Minerals of Canada, Economic Geology Series no. 1, 4th edition, 1957, Geological Survey of Canada, Ottawa.

47

My Hobby is Collecting Rocks and Minerals by David E. Jensen (Hart Book Company, Inc.). Getting Acquainted with Minerals by George English and David E. Jensen (McGraw-Hill Book Co. Inc.). A Field Guide to Rocks and Minerals by Frederick H. Pough ( Houghton Milllin Company). The World We Live In (Life Magazine, Time Inc.; distributed by Musson Book Company Ltd.).

48

Glossary

(p. 17). A time in the mid Precambrian Era when magma in tremendous volume invaded older rocks ( Couchiching, Keewatin, and Windigokan) to form mostly the rock known as granite. ANIMIXIE (p. 23). A period of time in the latter part of the Precambrian Era when the seas covered a part of western Ontario. AQUAMARINE (p. 39). Blue beryl. AUGITE. A shiny greenish-black mineral of complex composition. BASALT (p. 15). Fine-grained, solidified lava composed of the minerals plagioclase and augite. It is one of the rocks included in the term trap. BERYL (p. 39). This mineral is a silicate of beryllium and aluminium, and is a principal source of the very light metal beryllium. BRUCITE (p. 37). A white soft mineral with the composition of magnesium hydroxide. CALCITE. A common mineral, it is glassy white to pink and splits readily along three planes. It is the carbonate of calcium. CAMBRIAN (p. 9). A period of time immediately following the Precambrian Era, in which the seas teemed with life. CHLORITE (p. 20). A green micaceous mineral formed by the alteration of hornblende or augite. CONGLOMERATE (p. 13). A consolidated gravel. coRDIERITE (p. 33). A silicate mineral produced from the muddy parts of sedimentary rocks which have been metamorphosed. coucmcHING (p. 11). A period of time in the early part of the Precambrian Era when the sea covered much of northALGOMAN

49

western Ontario and sedimentary materials were deposited on the sea floor. The various rocks derived from these materials are now known as the Couchiching Series (p. 12). CRUST. The relatively thin ( a few miles only in thickness) outer layer of our earth. DIABASE (p. 24). A coarse-grained, very dark grey to black igneous rock composed of plagioclase and augite or a similar mineral.

(p. 20). An intrusion of igneous rock in a crack or fissure of the earth's crust. DIORITE (p. 21). A coarse-grained intrusive rock usually dark grey in colour and consisting of plagioclase and hornblende. EMERALD (p. 39). Green beryl. ERA (p. 8). The length of time necessary for a great geologic event or series of related geologic events which were of world-wide significance. FAULT (p. 41). A break in the earth's crust along which there has been movement of the two sides relative to one another. FELDSPAR (p. 21). A family or group of similar minerals which are all silicates of aluminium and sodium, potassium, or calcium. They are usually light-coloured and split readily along two planes at almost right angles. FOSSn. (p. 27). The petrified remains of an animal or plant. GABBRO (p. 21). A coarse-grained intrusive rock of usually dark grey colour and consisting of augite and plagioclase. GLACIAL STRIAE (p. 41). The scratches and grooves carved in the bedrock by the fragments of rock carried in the bottom of DIX:E

the glacier.

(p. 44). The wearing away of the bedrock and the transporting of the eroded material by a glacier. GLACIBR (p. 28). Now usually a river of ice, but in past geological times, sheets or ' seas" of ice possibly many thousands of feet thick. GNEISS (p. 22). A coarsely laminated rock produced by pressure on rocks such as granite. GOETHITE (p. 39). The brown hydrous oxide of iron. GRANITE (p. 21). A coarse-grained light grey to pink intrusive rock composed of quartz, orthoclase, and a little mica. GLACIATION

50

GREENSTONE (p. 20). A fine-grained green rock produced by metamorphism of basalt. GREENSTONE scmsT ( p. 20) . Thinly laminated greenstone. HEMATITE (p. 35). The red oxide of iron. HORNBLENDE. A shiny greenish-black mineral of complex composition. IGNEOUS (p. 24). An adjective referring to processes or rocks connected with magma or lava. Derived from the Creek word for "fire." IRON FORMATION (p. 15). A sedimentary rock composed of alternate bands of jasper, quartz, and magnetite. JASPER (p. 15). A red opaque mineral belonging to the quartz family. KAOLIN (p. 19). A hydrous aluminium silicate, the principal constituent of mud. KEEWATIN (p. 14). A period of time in the early part of the Precambrian Era when there was tremendous volcanic activity; lava poured out of countless vents and fissures, covering much of the country to great depths. See also p. 24. KEWEENAWAN (p. 24). A period of time at the end of the Precambrian Era in which there was igneous activity. LAVA (p. 7). Molten or liquid rock which pours out on the surface of the earth. MAGMA (p. 6). Molten or liquid rock located beneath the surface of the earth. MAGNETITE (p. 15). A black metallic mineral composed of iron oxide. METAMORPHOSED (p. 18). Changed-as applied to rocks which have been subjected to great pressure and or heat. MINERAL. Inorganic chemical substance usually of crystalline structure which occurs in nature. MOLYBDENITE (p. 39). A soft, flexible, silver-grey metallic mineral which is the sulphide of molybdenum. MORAINE (p. 30). Rock debris left behind as the ice of a glacier melts. NEMALITE (p. 37). A white fibrous variety of brucite. ORE (p. 24). A body of mineral matter which contains some 51

mineral substance of sufficient quantity to pay for extracting it. ORTHOCLASE. A light-coloured silicate belonging to the feldspar family. PEGMATITE (p. 21). A dike rock composed of quartz and feldspar in which the mineral grains are very large ( one inch to several feet in dimension) . PERIDOTITE (p. 21). A coarse-grained very dark intrusive rock composed of augite or other similar minerals. PERIOD (p. 8). The length of time involved in the great advance of the sea over the land and its eventual withdrawal. PLAGIOCLASE. A light-coloured silicate mineral of the feldspar family. PRECAMBRIAN ERA (p. 10). All time prior to the appearance of abundant life (Cambrian Period) on the earth. The length of this time is not known but is probably two billion ( two thousand million) years, and ended about five hundred million years ago. PRECAMBRIAN SHIELD (p. 10). The vast area of exposed Precambrian rocks. In North America it is also known as the Canadian Shield. QUARTZ (p. 18). A common glassy colourless mineral with a composition silicon dioxide. QUARTZITE (p. 18). Metamorphosed sandstone. ROCK. A relatively large mass of material consisting of one or more minerals. SANDSTONE (p. 13). Consolidated sands. SCWST (p. 19). Thinly laminated rock produced by pressure on impure sediments or volcanics. SEDIMENTARY ROCKS (p. 23). Rocks produced through deposition or precipitation from water; for example, sandstone. SERIES (p. 8) . A group of sedimentary rocks laid down during a period of geologic time. SERPENTINE (p. 37). A green, soft, somewhat slippery-feeling silicate mineral. SHALE (p. 13). Consolidated mud. SILICEOUS. High in silica ( silicon dioxide), i.e. quartz.

52

(p. 20). Intrusion of igneous rock between beds of sedimentary or volcanic rock. SLATE (p. 19). Metamorphosed shale. SPODUMENE (p. 38). A white to light greenish glassy mineral with a composition lithium aluminium silicate. STRATA. Plural of stratum. STRATUM, A layer or bed of sedimentary material deposited in water. TABULAR (p. 20). Flat or plate-like. TALC (p. 34). A soft white to green silicate mineral which feels soapy to the touch. TEMISKAMING SERIES. See under Windigokan, and p. 17. TRAP (p. 15). A general term for fine-grained dark coloured solidified lava. VEIN (p. 21). A thin, tabular body of mineral matter, usually quartz or calcite, deposited from solution in a crack or fissure. VULCANISM (p. 44). The outpouring of lava and other materials of volcanic origin from vents in the earth's crust. WINDIGOKAN (p. 16). A period of time in the early part of the Precambrian Era when the sea covered parts of northwestern Ontario and deposited sediments (Windigokan Series, p. 16) on the Keewatin lavas and Couchiching sediments. SILL

53

Acknowledgements

acknowledgement is made to the Quetico Foundation for their courtesy and help in the production of this volume, and to Dr. W. M. Tovell, Curator of Geology, Royal Ontario Museum, for his assistance in the preparation of the manuscript. The GeologicaJ Map used as endpapers was adapted from Map 222A, second edition, Department of Mines and Resources, Ottawa, by Mr. Bruce Harding, A.O.C.A., of the Ontario Department of Lands and Forests. GRATEFUL

54

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