The beach between Cape Hearne and Cape Kendall is in some places composed of slate-clay, and of a clay resembling wacke. Many large boulders of greenstone occur there. Cape Kendall is a projecting rocky point, about five or six hundred feet high, and nearly precipitous on three sides, which are washed by the sea. On the north, its rocks consist entirely of greenstone, but on the south side of the Cape the greenstone in lofty columns reposes on thin-slaty beds of fine-grained, bluish-gray limestone. Back"s Inlet presents on each side a succession of lofty precipitous headlands, which have the shape termed, by seamen, "the gunner"s quoin." Most of the islands and points near the mouth of the Coppermine have this form, and are composed of trap rocks.
[Sidenote: 220] One of Cowper"s islands on which we landed consists of beds of greenstone cropping out like the steps of a stair.
A low ridge of greenstone exists at the mouth of the Coppermine river, and from thence to b.l.o.o.d.y-fall, a distance of ten miles, the country is nearly level, with the exception of some low ridges of trap which run through it. The channel of the river is sunk about one hundred and fifty feet below the surrounding country, and is bounded by cliffs of yellowish white sand, and sometimes of clay, from beneath which, beds of greenstone occasionally crop out.
At b.l.o.o.d.y-fall, a round-backed ridge of land, seven or eight hundred feet high, crosses the country. It has a gentle ascent on the north, but is steep towards the south. The river at the fall makes its way through a narrow gap, whose nearly precipitous sides consist of tenacious clay, the bed and immediate borders of the stream being formed of greenstone.[45] From thence to the Copper Mountains, gently undulated plains occur, intersected in various parts by precipitous ridges of trap rocks, and the river flows in a narrow chasm, sunk about one hundred feet below their level. A few miles above b.l.o.o.d.y-fall, strata of light gray clay-slate, dipping to the north-east, at an angle of 20 degrees, support some greenstone cliffs on the banks of the river. [Sidenotes: 222, 223, 224] From this place to the Copper Mountains the rocks observed in the ravines were a dark reddish-brown, felspathose sandstone, and gray slate-clay, in horizontal strata, with greenstone rising in ridges. The soil is sandy, and in many places clayey, with a pretty close gra.s.sy sward. Straggling spruce trees begin to skirt the banks of the river about eighteen or twenty miles from the sea.
COPPER MOUNTAINS.
The Copper Mountains rise perhaps eight or nine hundred feet above the bed of the river, and at a distance, present a somewhat soft outline, but on a nearer view they appear to be composed of ridges which have a direction from W.N.W. to E.S.E. Many of the ridges have precipitous sides, and their summits, which are uneven and stony, do not rise more than two hundred, or two hundred and fifty feet above the vallies, which are generally swampy and full of small lakes. The only rocks noticed when we crossed these hills on the late journey, were clay-slate, greenstone, and dark red sandstone, sometimes containing white calcareous concretions, resembling an amygdaloidal rock. On our first journey down the Coppermine River, we visited a valley where the Indians had been accustomed to look for native copper, and we found there many loose fragments of a trap rock, containing native copper, green malachite, copper glance, and iron-shot copper green; also trap containing greenish-gray prehnite with disseminated native copper, which, in some specimens was crystallized in rhomboidal dodecahedrons.
Tabular fragments of prehnite, a.s.sociated with calc-spar and native copper, were also picked up, evidently portions of a vein, but we did not discover the vein in its original repository. The trap-rock, whose fragments strewed the valley, consists of felspar, deeply coloured by hornblende. A few clumps of white spruce trees occur in the vallies of the Copper Mountains, but the country is in general naked. The Coppermine River makes a remarkable bend round the end of these hills.
After quitting the Copper Mountains, and pa.s.sing a valley occupied by a chain of small lakes in lat. 67 degrees 10 minutes, long. 116 degrees 45 minutes, we travelled over a formation whose prevailing rocks are spotted sandstone and conglomerate, and which forms the _height of land_ betwixt Bear Lake and the Coppermine River. The ascent to this height from the eastward is gradual, but the descent towards Bear Lake is more rapid. The country is broken and hilly, though the height of the hills above the sea is perhaps inferior to that of the Copper Mountains. The vallies through which the small streams that water the country flow, are narrow and deep, resembling ravines, and their sides are clayey. The ground is strewed with gravel.
The _sandstone_ has very generally a purplish colour, with gray spots of various magnitudes. It is fine grained, hard, has a somewhat vitreous l.u.s.tre and contains little or no disseminated mica.
The _conglomerate_ consists of oval pebbles of white quartz, sometimes of very considerable magnitude, imbedded in an iron-shot cement. Many of the pebbles appear as if they had been broken and firmly re-united again. The conglomerate pa.s.ses into a coa.r.s.e sandstone.
Porphyry and granite form hills amongst the sandstone strata.
The _porphyry_ has a compact basis, like hornstone, of a dull brown colour, which contains imbedded crystals of felspar and quartz, and occasionally of augite. It forms some dome-shaped and short conical hills.
The _granite_ is disposed in oblong ridges, with small mural precipices.
It has, generally, a flesh-red colour, and contains some specks of augite, but little or no mica. The granite and porphyry were observed only on the east side of the height of land, the brow of which, and its whole western declivity, is formed of sandstone. Boulders of granite and porphyry, precisely similar to the varieties which occur _in situ_ on the height of land, are common on the beach at Fort Franklin, and on the banks of the Mackenzie above Bear Lake.
To the westward of the height of land, the country on the banks of Dease River is more level, and few rocks _in situ_ were seen, until within five or six miles of Bear Lake, where the stream flows through a chasm, whose sides are composed of a soft, fine-grained red sandstone, like that which occurs in the vale of Dumfries, in Scotland. Several ravines here have their sides composed of fine sand, inclosing fragments of soft sandstone.
About three miles from the mouth of Dease River we came to a limestone formation, which has been already noticed in the account of the geological structure of the sh.o.r.es of Great Bear Lake.
EASTERN CHAIN OF PRIMITIVE ROCKS.
The preceding part of the paper describing the rock formations which were noticed on the route of the expedition from Great Slave Lake down the Mackenzie along the sh.o.r.es of the Arctic Sea, the Coppermine, Great Bear Lake, and Great Bear River, being a distance of three thousand miles, I shall, by way of supplement, mention very briefly some of the more southern deposits.
The first I have to speak of is the chain of primitive rocks to which I have alluded in page 289, as extending for a very great distance in a north-west direction, and inclining in the northern parts slightly towards the Rocky Mountain Chain. Dr. Bigsby, in his account of the geology of Lake Huron says, that "The primitive rocks on the northern sh.o.r.es of that lake are part of a vast chain, of which the southern portion, extending probably uninterruptedly from the north and east of Lake Winipeg, pa.s.ses thence along the northern sh.o.r.es of Lakes Superior, Huron, and Simcoe, and after forming the granitic barrier of the Thousand Isles, at the outlet of Lake Ontario, spreads itself largely throughout the state of New York, and there joins with the Alleghanies, and their southern continuations." It is not my intention to say any thing further of the rocks in the districts of which Dr. Bigsby speaks, although in travelling from the United States to Lake Winipeg the expedition pa.s.sed over them. That zealous geologist has already given, in various publications, many interesting and accurate details of the formations on the borders of the great lakes; an account of those which lie some degrees farther to the north is inserted in the second volume of the Geological Transactions,--and there are some notices of them in the Appendix to the narrative of Captain Franklin"s First Journey. My object at present is, merely to trace the western boundary of the primitive rocks in their course through the more northerly parts of the American continent.
I have already quoted Sir Alexander Mackenzie"s original and important remark, of the princ.i.p.al lakes in those quarters being interposed betwixt the primitive rocks and the secondary strata, lying to the westward of them--Lake Winipeg is an instance in point. It is a long, narrow lake, and is bounded throughout on its east side by primitive rocks, mostly granitic, whilst its more indented western sh.o.r.e is formed of horizontal limestone strata. The western boundary of the primitive rocks, extending on this lake about two hundred and eighty miles, has nearly a north-north-west direction. From Norway Point, at the north end of the lake, to Isle a la Crosse, a distance of four hundred and twenty miles in a straight line, the boundary has a west-north-west direction.
For two hundred and forty miles from Isle a la Crosse to Athabasca Lake, the course of the primitive rocks is unknown to me; but from Athabasca Lake to M"Tavish"s Bay, in Great Bear Lake, a distance of five hundred miles, their western edge runs about north-west-by-west, and is marked by the Slave River, a deep inlet on the north side of Great Slave Lake, and a chain of rivers and lakes, (including great Marten Lake,) which discharge themselves into that inlet.
Captain Franklin on his voyage crossed this primitive chain nearly at right angles to its line of direction, in proceeding from Hudson"s Bay to Lake Winipeg--it was there two hundred and twenty miles wide.
The hills composing the chain are of small elevation, none of them rising much above the surrounding country. They have mostly rounded summits, and they do not form continuous ridges; but are detached from each other, by vallies of various breadth, though generally narrow, and very seldom level. The sides of the hills are steep, often precipitous.
When the vallies are of considerable extent, they are almost invariably occupied by a lake, the proportion of water in this primitive district being very great; from the top of the highest hill on the Hill River, which has not a greater alt.i.tude than six hundred feet, thirty-six lakes are said to be visible. The small elevation of the chain may be inferred from an examination of the map, which shows that it is crossed by several rivers, that rise in the Rocky Mountains, the most considerable of which are the Churchill and the Saskatchewan, or Nelson River. These great streams have, for many hundred miles from their origin, the ordinary appearance of rivers, in being bounded by continuous parallel banks; but on entering the primitive district, they present chains of lake-like dilatations, which are full of islands, and have a very irregular outline. Many of the numerous arms of these expansions wind for miles through the neighbouring country, and the whole district bears a striking resemblance, in the manner in which it is intersected by water, to the coast of Norway and the adjoining part of Sweden. The successive dilatations of the rivers have scarcely any current, but are connected to each other by one or more straits, in which the water-course is more or less obstructed by rocks, and the stream is very turbulent and rapid. The most prevalent rock in the chain is gneiss; but there is also granite and mica-slate, together with numerous beds of amphibolic rocks.
LIMESTONE OF LAKE WINIPEG.
To the westward of the chain of primitive rocks, through a great part, if not through the whole of its course, lies an extensive horizontal deposit of limestone.
Dr. Bigsby, in the Geological Transactions, has described, in detail, the limestone of Lake Huron, and is disposed to refer "the cavernous and brecciated limestone of Michilimackinac to the magnesian breccia, which is in England connected with the red marl;" whilst the limestones of St.
Joseph, and the northern isles, he considers as more resembling the well-known formation of Dudley, in Staffordshire. The limestone of Thessalon Isle, in which there occurs the remarkable species of orthocerat.i.te which he has figured, he describes as decidedly magnesian.
I observed this orthocerat.i.te in the limestone strata of one of the isles forming the pa.s.sage of La Cloche in Lake Huron. The limestone deposits of Lake Winipeg and Cape Parry exactly resemble that of La Cloche in mineralogical characters, and in containing the same orthocerat.i.te which was also found by Captains Parry and Lyon at Igloolik.
The colour of the limestone of Lake Winipeg is very generally yellowish-white, pa.s.sing into buff, on the one hand, and into ash-gray on the other. A reddish tinge is also occasionally observed. Much of it has a flat fracture, with little or no l.u.s.tre, and a fine-grained arenacious structure. A great portion of it, however, is compact, and has a flat conchoidal and slightly splintery fracture. This variety pa.s.ses into a beautiful china-like chert. [Sidenote: 1001, 1014] Many of the beds are full of long, narrow vesicular cavities, which are lined sometimes with calc-spar, but more frequently with minute crystals of quartz. The beds of this formation seldom exceed a foot in thickness, and are often very thin and slaty. The arenacious and cherty varieties frequently occur in the same bed; sometimes they form distinct beds. The softer kinds weather readily into a white marl, which is used by the residents to whitewash their houses. Wherever extensive surfaces of the strata were exposed, as in the channels of rivers, they were observed to be traversed by rents crossing each other at various angles. The larger rents, which were sometimes two yards or more in width, were however, generally parallel to each other for a considerable distance.
Professor Jameson enumerates _terebratulae_, _orthocerat.i.tes_, _encrinites_, _caryophyllitae_, and _lingulae_, as the organic remains in the specimens brought home by Captain Franklin on his first expedition.
Mr. Stokes and Mr. James De Carle Sowerby have examined those which we procured on the last expedition, and found amongst them _terebratulites_, _spirifers_, _maclurites_, and _corallines_. The maclurites belonging to the same species, with specimens from Lakes Erie and Huron, and also from Igloolik, are perhaps referrible to the _Maclurea magna_ of Le Sueur. [Sidenote: 1015, 1019] Mr. Sowerby determined a sh.e.l.l, occurring in great abundance in the strata at c.u.mberland-house, about one hundred and twenty miles to the westward of Lake Winipeg, to be the _Pentamerus Aylesfordii_.
The extent to the westward of the limestone deposit of Lake Winipeg is not well known to me; but I have traced it as far up the Saskatchewan as Carlton House, and its breadth there is at least two hundred and eighty miles. For about one hundred miles below Carlton House, the river Saskatchewan flows betwixt banks from one to two hundred feet in height, consisting of clay or sand, and the beds of limestone are exposed in very few places. The plains in the neighbourhood of Carlton abound in small lakes, some of which are salt. The country which the Saskatchewan waters for one hundred and ninety miles before it enters Lake Winipeg, is of a different kind. It is still more flat than that about Carlton, and is so little raised above the level of the river, that in the spring-floods the whole is inundated, and in several places the river sends off branches which reunite with it after a course of many miles.
In this quarter the soil is generally thin, and the limestone strata are almost every where extensively exposed. To the southward of c.u.mberland House, the Basquiau Hill has considerable elevation. I had not an opportunity of visiting it; but in the flat limestone strata, near its foot, there are salt springs, from which the Indians sometimes procure a considerable quant.i.ty of salt by boiling; and there are several sulphureous springs within the formation.
I observed no beds of conglomerate in it, and no sandstone a.s.sociated with it; but the extensive plains which lie betwixt Carlton House and the Rocky Mountains are sandy, and beds of sandstone are said to be visible in some of the ravines.
The line of contact of the limestone with the primitive rocks of Lake Winipeg, is covered with water; but at the Dog"s-Head, and near the north end of Beaver Lake, they are exposed within less than a mile of each other. To the southward of the Dog"s-Head in Lake Winipeg, and in a few other quarters, some schistose rocks, belonging to the transition series, are interposed between the two formations.
Before quitting the formations of Lake Winipeg, I may remark, that the height of that lake above the sea is perhaps equal to that of Lake Superior, which is eight hundred feet.
LIMESTONE OF THE ELK AND SLAVE RIVERS.
The next formation I have to mention is one which appears to possess most of the characters ascribed by German geologists to the zechstein.
It extends from the north side of the Methy carrying-place down the Clearwater, Elk, and Slave Rivers, and along the south sh.o.r.e of Great Slave Lake to the efflux of the Mackenzie. The line I have traced was the route of the expedition, and is also very nearly that of the eastern boundary of the limestone. Primitive rocks occur in Lake Mammawee, Athabasca Lake, and on the Stony River; and on several parts of the Slave River they are separated from the limestone only by the breadth of the stream. On Great Slave Lake, the Stony Island, on the north-east side of the mouth of Slave River, is composed of granite, whilst the limestone strata are exposed at Fort Resolution on the south-west side.
[Sidenote: 1027, 1028] The limestone in this extensive tract is commonly in thin and nearly horizontal beds, and much of it exactly resembles in mineralogical characters the dolomite and chert of Lake Winipeg. It is interstratified with thin beds of soft white marl; and in a few places with a marly sandstone. Extensive beds of stinkstone also occur, and many beds of limestone containing fluid bitumen in cavities. The bitumen is in such quant.i.ty, in some quarters, as to flow in streams from fissures in the rock; and in an extensive district, around Pierre au Calumet on the Elk River, slaggy mineral pitch fills the crevices in the soil, and may be collected in large quant.i.ties by digging a well.
A calcareous breccia also exists in various places, particularly on the Slave River. Springs depositing from their waters sulphur, and sulphate of lime, slightly mixed with sulphate of magnesia, muriate of soda, and iron, are common and copious. A few miles to the westward of the Slave River, there is a ridge of hills several miles long, and about two hundred feet high, having several beds of compact, grayish gypsum exposed on its sides. From the base of this hill there issue seven or eight very copious, and many smaller springs, whose waters deposit a great quant.i.ty of very fine muriate of soda by spontaneous evaporation.
The collected rivulets from these springs form a stream which is, at its junction with the Slave River, sixty yards wide and eight or ten feet deep.
[Sidenote: 1020 to 1026] The organic remains, in this deposit, according a list kindly furnished by Mr. Sowerby, consist of _spirifers_, [Sidenote: 1029 to 1032] one of which is the _spirifer acuta_; several new _terebratulae_, of which one resembles the _T. resupinata_, a _cirrus_, some crinoidal remains, and corals.
At the union of Clearwater and Elk Rivers, the limestone beds are covered to the depth of one hundred and fifty feet with bituminous shale.
I have stated, that on Slave River this limestone formation succeeds immediately to primitive rocks, but I am not acquainted with the rocks that lie to the eastward of it on the Elk River. The traders report that there are extensive deposits of sandstone on the eastern arm of the Athabasca Lake, and, perhaps, these sandstones extend nearly to Clearwater River. Sand covers the limestone on that river to the depth of eight or nine hundred feet, and the fragments of sandstone in it are large, numerous, and not worn.
The quant.i.ty of gypsum in immediate connection with extremely copious and rich salt springs, and the great abundance of petroleum in this formation, together with the arenacious, soft, marly, and brecciated beds interstratified with the dolomite, and above all, the circ.u.mstance of the latter being by far the most common and extensive rock in the deposit, led me to think that the limestone of the Elk and Slave Rivers was equivalent to the zechstein of the continental geologists. My opinion, however, on this subject is, from a total want of practical acquaintance with the European rock formations, of little weight; and several eminent geologists are, after an examination of the organic remains and mineralogical characters of the specimens brought home, inclined to consider the formation as a.n.a.logous to the carboniferous or mountain-limestone of England.
As to the limestone formation of Lake Winipeg, I have no doubt of its ident.i.ty with that occurring in the islands at the pa.s.sage of La Cloche, in Lake Huron, and also with that at Cape Parry and at Cape Krusenstern, on the coast of the Arctic Sea. It is probable, also, that these four deposits belong to the same epoch with the limestone of Elk and Slave Rivers, although they differ in containing little or no petroleum. It is proper to mention, however adverse it may be to the opinion I have ventured to hint at above, of these extensive horizontal deposits of limestone being referable to the zechstein, that the limestone of Lake Huron is generally considered as belonging to the mountain-limestone; and Professor Jameson, from a review of the organic remains occurring in the Lake Winipeg deposit, considered that it also belonged to that formation. The formation of Cape Lyon may be, with less danger of a mistake, referred to the transition or mountain-limestone.
THE END.
[Ill.u.s.tration]
FOOTNOTES:
[20] This was estimated by allowing one foot descent per mile for Bear Lake River, whose length is seventy miles; and three inches per mile for the descent of Mackenzie River, from the junction of the former river to the sea, being a distance of five hundred miles.
[21] In our former journey, we sounded near the Rein-Deer Islands in Slave Lake, with sixty-five fathoms line, without reaching the bottom.
[22] Section of the cliffs at Limestone Point--strata dipping to the N.N.W.