Narrative of a Second Expedition to the Shores of the Polar Sea Part 17

The Bear Lake River flows into the Mackenzie at a right angle, and on its north bank, at its mouth, there is a hill, which has been already noticed as forming part of a ridge visible from the one at the rapid, with which it probably unites to form a great basin. These two hills seem to belong to the same formation. [Sidenote: 61, 62, 60] The body of the hill consists of highly-inclined beds of blackish-gray limestone, with sparry veins, and of brownish-gray dolomite, which cannot be distinguished in hand specimens from that of the hill at the rapid. The superior beds are formed of a calcareous breccia.[27] [Sidenote: 57, 58, 59, 63, 64, 65] a.s.sociated with these strata, however, there are beds of limestone, highly charged with bitumen; and at the base of the hill there are beds of bituminous shale, some of which effervesce with acids, whilst others approach in hardness, and other characters, to flinty slate. These shaly beds were seen by Captain Franklin and Mr.

Kendall in autumn 1825, and they also saw, at that time, some sulphureous springs and streams of mineral pitch issuing from the lower parts of the limestone strata: but the whole of them were hid by the height of the waters of the Mackenzie in the spring of 1826.[28]

[Sidenote: 69, 66, 67, 68] The same cause prevented me from seeing some beds of lignite and sandstone, at the same place, of which Captain Franklin obtained specimens.

LIGNITE FORMATION.--MACKENZIE'S RIVER.

Having noticed the general features of this portion of the river, I have next to state, that the formation const.i.tuting its banks may be characterized as consisting of wood-coal in various states, alternating with beds of pipe-clay, potter's clay, which is sometimes bituminous, slate-clay, gravel, sand, and friable sandstones, and occasionally with porcelain earth. The strata are generally horizontal, and as many as four beds of lignite are exposed in some parts, the upper of which are above the level of the highest river-floods of the present day.

The _lignite_, when recently detached from the beds, is pretty compact, but soon splits into rhomboidal pieces, which again separate into slates more or less fine. It burns with a very fetid smell, somewhat resembling that of phosphorus, with little smoke or flame, leaving a brownish-red ash, not one-tenth of the original bulk of the coal. The blacksmith found it unfit for welding iron when used alone, but it answered when mixed with charcoal, although the stench it created was a great annoyance. [Sidenote: 48] Different beds, and even different parts of the same bed, presented specimens of the fibrous brown-coal, earth-coal, conchoidal brown-coal, and trapezoidal brown-coal of Jameson. Some of the pieces have the external appearance of compact bitumen, but they generally exhibit, in the cross fracture, the fibrous structure of wood in concentric layers, apparently much compressed. Other specimens have a strong external resemblance to charcoal in structure, colour, and l.u.s.tre. A frequent form of the lignite is that of slate, of a dull, brownish-black colour, but yielding a s.h.i.+ning streak. The slate is composed of fragments, resembling charred wood, united together by a paste of more comminuted woody matter, mixed, perhaps, with a small portion of clay. In the paste there are some transparent crystals of sulphate of lime, and occasionally some minute portions of a substance like resin. These shaly beds bear a strong resemblance to peat, not only in structure but also in the mode of burning, and in the light whitish ashes which are left. The external shape of stems or branches of trees, is best preserved in some fragments impregnated with slate-clay, and occasionally with siliceous matter, which occur imbedded in the coal.

The bark of these pieces has been converted into lignite. Some of them exhibit knots, such as occur where a branch has decayed, and others represent the twists and contortions of wood of stunted growth. The lignite is generally penetrated by fibrous roots, probably _rhizomorpha_, which insinuate their ramifications into every crevice.

The beds of lignite appear to take fire spontaneously when exposed to the atmosphere. They were burning when Sir Alexander Mackenzie pa.s.sed down the river in 1789, and have been on fire, in some part or other of the formation, ever since. In consequence of the destruction of the coal, large slips of the bank take place, and it is only where the debris has been washed away by the river that good sections are visible.

The beds were on fire when we visited them, and the burnt clays, vitrified sand, agglutinated gravel, &c. gave many spots the appearance of an old brick-field.

[Sidenote: 81] The _gravel_ interstratified with the lignite, consists of smooth pebbles of Lydian stone, of flinty slate, of white quartz, of quartzose sandstone, and conglomerate, like the sandstones and conglomerates of the old red sandstone formation, of claystone, and of slate-clay, varying in size from a pea to that of an orange. The gravel is often intermixed with a little clay, which gives the bed sufficient tenacity to form cliffs, but does not prevent the pebbles from separating, in the attempt to break off hand specimens. It is seamed by thin layers of fine sand: beds of sandstone are of occasional occurrence.

_Potter's clay_ occurs in thick beds, has generally a gray or brown colour, and pa.s.ses, in some places, into a highly bituminous thick-slaty clay, penetrated by ramifications of carbonaceous matter resembling the roots of vegetables.

The _pipe-clay_ is deserving of particular notice. It is found in beds from six inches to a foot thick, and mostly in contact with the lignite.

It has commonly a yellowish-white colour, but in some places its hue is light lake-red. The natives use it as an article of food in times of scarcity and it is said to have sustained life for a considerable time.

It is termed _white mud_ by the traders, who whitewash their houses with it. It occurs also in lignite deposits on the upper branches of the Saskatchewan, and is a.s.sociated with bituminous shale on the coast of the Arctic Sea. Mr. Nuttall mentions a similar substance, under the name of pink-clay, as being found in the lignite deposits on the Arkansa.[29]

The _porcelain earth_ was observed only at one place where the beds were highly inclined, and there it appeared to replace the sandstones of other parts of the deposit. It has a whitish colour, and the appearance, at first sight, of chalk; but some of its beds, from the quant.i.ty of carbonaceous matter interspersed through them, having a grayish hue. Its beds are from two to three yards thick.

In a note[30] I have mentioned the most remarkable sections of this formation which occur on the banks of the Mackenzie. The depth of the formation was not ascertained, but the sections will show the thickness of the beds which were exposed. The height above the sea of the summit of the banks it forms on the Mackenzie, was estimated to be from two hundred and fifty to three hundred feet.

NOTICES OF OTHER LIGNITE FORMATIONS.

Similar formations of lignite occur near the foot of the Rocky Mountain range farther to the southward; but I have not, after many inquiries, heard of any traces of them in the eastern parts of the Hudson's Bay lands. Sir Alexander Mackenzie, after describing the general course of the Rocky Mountains, says that "along their eastern edge, there occurs a narrow strip of marshy, boggy, and uneven ground, which produces coal and bitumen;" and that "he saw these on the banks of the Mackenzie in lat. 66 degrees, and, in his second journey, on the Peace River, in lat.

56 degrees and 146 degrees W. long.;" and further, that "the same was observed by Mr. Fidler, on the south branch of the Saskatchewan, in lat.

52 degrees long. 112-1/2 degrees W." Mr. Alexander Stewart, an intelligent chief factor of the Hudson's Bay Company, and well acquainted with those countries, informs me that there are beds of coal on fire, on the Smoking River, or east branch of the Peace River, and on the upper parts of the _Riviere la b.i.+.c.he_, or Elk River; and that coal, although not on fire, occurs at Lesser Slave Lake, on a line with the other two localities. Mr. Small, a clerk to the Hudson's Bay Company, likewise acquaints me, that coal occurs at Edmonton, on the north branch of the Saskatchewan, in beds, sometimes seven or eight feet thick. Most of the coal is thin-slaty; but some beds yield s.h.i.+ning, thick lumps, which break, as he expresses it, like Spanish liquorice. It lies over beds of bluish-gray sandstone, and is a.s.sociated with a white clay, which froths in water and adheres to the fingers.

Mr. Drummond brought specimens from the spot which Mr. Small alludes to and remarks, that the lignite occurs in beds from six inches to two feet thick, separated by clay and sandstones. [Sidenote: 1051, 1052, 1053]

His specimens of the lignite are precisely similar to the slaty and conchoidal varieties, which occur at the mouth of the Bear Lake River; [Sidenote: 1055] and there is an equal resemblance betwixt the sandstones from the two places. [Sidenote: 1053] The slaty beds of lignite, at Edmonton, pa.s.s into a thin, slaty, friable sandstone, much impregnated by carbonaceous matter, and containing pieces of fibrous lignite. [Sidenote: 1056, 1062] In the neighbourhood of the lignite there are some beds of rather indurated, but highly bituminous shale, and the clayey banks contain clay-iron stones, in form of septaria. Mr.

Drummond likewise found beds of a beautiful bituminous coal, which Professor Buckland, from its peculiar fracture, considers to be tertiary pitch-coal. [Sidenote: 1058, 1059, 1060] The banks of the Saskatchewan, near the same place, exhibit beds of a very compact stone, having a brown colour, and inclosing many fragments of bituminous limestone and some organic remains; likewise beds of a somewhat similar stone, but full of drusy cavities, and more resembling a recent calcareous tufa. I could not learn how far these beds were connected with the lignite deposit.

Captain Franklin[31] saw beds of lignite and tertiary pitch-coal at Garry's Island, off the mouth of the Mackenzie, and there is an extensive deposit of it near the Babbage River, on the coast of the Arctic Sea, opposite to the termination of the Richardson chain of the Rocky Mountains.

MACKENZIE RIVER FROM SLAVE LAKE TO THE BASE OF THE ROCKY MOUNTAINS.

Having now described the strata in Bear Lake River, together with the exposed beds of the lignite at its mouth, as far as opportunities of observation enable me, and also added a slight account of similar formations which occupy a like situation at the foot of the Rocky Mountain range, were I to adapt the order of my notices strictly to the route of the expedition, I should next describe the banks of the Mackenzie from the junction of the Bear Lake River downwards to the Arctic Sea. It seems, however, more advisable to commence at the origin of the Mackenzie, in Great Slave Lake, and give as connected a view as I can of the princ.i.p.al geological features of that great river.

The west end of Slave Lake is bounded by horizontal strata of a limestone, whose characters shall be afterwards given in detail; and I have merely to remark, at present, that it forms flat sh.o.r.es, which are skirted by shoals of boulders of limestone, and of primitive rocks. Much drift timber is acc.u.mulated in the small bays at this end of the lake, which, in process of time, is converted into a substance like peat. A chain of islands extends obliquely across the lake at the origin of the river, or where the current is first felt; and the depth of the water there is less than six feet. Below this, there is a dilatation termed the _first little lake_, and the river afterwards contracts to less than a mile in breadth; forming in one place, when the water is low, a strong rapid. A second dilatation, about twenty-five miles below the first, is termed the _second little lake_. The sh.o.r.es throughout this distance are generally flat and covered with boulders of limestone, compact felspar, granite, gneiss, and sienite, and there are many of these stones imbedded in a tenacious clay, which forms the beach. A ridge, having an even outline, and apparently of small elevation, commences behind Stony Point, in Slave Lake, some distance inland, and, running nearly parallel to the river, disappears about Fis.h.i.+ng River, a stream which joins the Mackenzie, below the Second Little Lake. The Horn Mountains, a ridge of hills, of considerably greater elevation, and having a more varied outline than that on the south sh.o.r.e, are first visible on the north side of the Second Little Lake, and continue in sight nearly as far as the junction of the "River of the Mountains," or "Forks, of the Mackenzie," as the traders term the union of the two rivers. [Sidenote: 120, 121] The only rocks seen _in situ_ between Slave Lake and the Forks, were a bituminous shale of a brownish-black colour, in thin slates, and a slate-clay of a pure yellowish-gray colour, which, as well as the bituminous shale, forms steep banks.

ROCKY MOUNTAINS.

About twenty-five or thirty miles below the forks, the first view is obtained of the Rocky Mountains, which there appear to consist of short-conical peaks, scarcely rising two thousand feet above the river.

Some distance lower down, the river, changing its course from W.N.W. to N.N.E., turns sharply round the mountains, which are there disposed in ridges, having bases from one to two miles wide, and a direction of S.S.W. or S.W. by S. being nearly at right angles to the general course of the great range to which they belong. The eastern sides of the ridges present a succession of wall-sided precipices, having beneath them shelving acclivities formed by debris, and exhibiting on their faces regular lines of stratification. The western sides of the ridges are of more easy ascent. The vallies which separate these ridges and open successively to the river, are narrow, with pretty level bottoms, but very steep sides well clothed with trees. In the first ridge, the strata seemed to dip to the northward at an angle of 35 degrees. In some of the others they were horizontal, or had a southerly dip. The third ridge presents, when viewed from the westward, a magnificent precipice, seemingly about one thousand two hundred feet high, and which extends for at least fifteen miles. After pa.s.sing this ridge, the river inclines to the eastward, and the forms of the hills are less distinctly seen.

As I could not visit the Rocky Mountains, I know nothing of their structure except from report. An interpreter in the Hudson's Bay Company's service, who had travelled over them, informed me that there are fourteen or fifteen ridges, of which the three easternmost are the most rugged, those that succeed being broader and more rounded.

[Sidenote: 122] This man gave me a specimen of a pearl-gray semi-opal, resembling obsidian, brought from the third or fourth ridge. The natives, by means of fire, cause this stone to break off in thin, flat, conchoidal fragments, with which they form arrow-heads and knives. The thin pieces are nearly transparent on the edges. [Sidenote: 123] He also gave me a specimen of plumbago, from the same quarter, and some specular iron.

Mr. Macpherson, of the Hudson's Bay Company, in a letter respecting the Rocky Mountains, near _Fort au Liard_, on the River of the Mountains, or south branch of the Mackenzie, informs me, that "these mountains may be traced into somewhat uniform ranges, extending north-westerly and south-easterly, nearly parallel with the River of the Mountains, and are in appearance confusedly scattered and broken, rising here and there into high peaks." [Sidenote: 124, 125] This gentleman had the kindness to send me specimens of a cherty rock, some of which, he states, were from the third range westward from the river, and others from a spur which projects in a southern direction from the fourth range, and rises about six hundred feet above the adjacent valley. These specimens cannot be distinguished from those of Limestone Point, on the north sh.o.r.e of Great Bear Lake[32], Mounts Fitton and Conybeare, two remarkable peaks which terminate the Eastern range of the Rocky Mountains on the sh.o.r.es of the Arctic sea, were found by Captain Franklin to consist of transition rocks, of which an account is given in the subjoined note.[33]

Sir Alexander Mackenzie, towards the conclusion of the interesting narrative of his voyages, says, of the Rocky Mountain range, "The last line of division is, the immense ridge, or succession of ridges of the stony mountains, whose northern extremity dips in the Arctic Sea in lat.i.tude 70 degrees north, and longitude 135 degrees west, running nearly south-east, and begins to be parallel to the coast of the Pacific ocean from Cook's inlet, and so onwards to the Columbia. From thence it appears to quit the coast, but still continuing with less elevation to divide the waters of the Atlantic from those of the Pacific. In these snow-clad mountains rises the Mississippi, if we admit the Missouri to be its source, which flows into the Gulph of Mexico; the river Nelson which is lost in Hudson's Bay; Mackenzie's river that discharges itself into the North Sea, and the Columbia emptying itself into the Pacific Ocean. The breadth of the mountains from Cook's inlet to the Columbia is from four to eight degrees easterly." I may add, that the great rivers mentioned by Mackenzie not only take their origin from the same range of mountains, but almost from the same hill; the head waters of the Columbia and Mackenzie being only about two hundred yards apart in lat.i.tude 54-1/2 degrees. Mr. Drummond, who crossed the mountains at that place, informs me, that the Eastern side of the range consists of conglomerate and sandstone, to which succeed limestone hills exceedingly barren, and afterwards clay-slate and granite.

James, the intelligent naturalist, who accompanied Major Long on his first expedition, says of the Rocky Mountains to the southward of the Missouri, "They rise abruptly out of the plains which lie extended at their base on the east side, towering into peaks of great height, which renders them visible at the distance of more than one hundred miles from their base. They consist of ridges, k.n.o.bs, and peaks, variously disposed, among which are interspersed many broad and fertile valleys.

James's peak, one of the more elevated, was ascertained by trigonometrical measurement to rise 8500 feet above the common level.

The rocky formations are uniformly of a primitive character, but a deep crust of secondary rocks appears to recline on the east side of the mountains, extending upwards from their base many hundred feet." In another place, he says, "The woodless plain is terminated by a range of naked and almost perpendicular rocks, visible at the distance of several miles, and resembling a vast wall parallel to the base of the mountain.

These rocks are sandstone, and rise abruptly to an elevation of one hundred and fifty or two hundred feet." The sandstone walls seem to present an appearance not very dissimilar to some of the cliffs seen from the Mackenzie.

Having thus mentioned as briefly as I could the extent of the information I was able to collect, respecting the Rocky Mountain range, I may remark, that a formation of primitive rocks, but little elevated above the general level of the country, appears to run from near the west end of Lake Superior, gradually and slightly converging towards the Rocky Mountains, until it attains the east side of Great Bear Lake. In lat. 50 degrees, the two ranges are nearly seven hundred miles apart, and there, and as far as lat. 60 degrees, the s.p.a.ce between them is princ.i.p.ally occupied by horizontal strata of limestone. There is also much limestone in the narrower interval north of 60 degrees, but the strata are more inclined, and form abrupt hills and ridges, particularly about lat. 66 degrees, where the primitive rocks on the east of Bear Lake are within two hundred miles of the Rocky Mountains. Sir Alexander Mackenzie has noticed that a chain of great lakes skirts this eastern range of primitive rocks, where they are approached by the flat limestone strata which lie to west of them. Thus the primitive rocks bound Great Slave Lake to the eastward of Slave River, and the flat limestone strata occupy the country westward of that lake, as has been already mentioned.

After this digression, which seemed necessary for the purpose of giving a general idea of the structure of the country, I return to the description of the banks of the Mackenzie.

MACKENZIE RIVER FROM THE FIRST SIGHT OF THE ROCKY MOUNTAINS TO BEAR LAKE RIVER.

At the sharp turn of the river round the Rocky Mountains, its east bank swells gently into a hill several feet high. Below this the banks are broken into conical ma.s.ses by ravines, and present a finely variegated outline. A pretty high ridge, looking like a continuation of the Horn Mountains, is visible on the east side some distance inland. Opposite to the Big Island there is a green hill three or four hundred feet high, which, as we descended the river, showed itself to be part of a range that had a direction apparently to the N.N.W., and towards its northern end became more rugged and craggy, exhibiting cliffs and rude embrasures, at the same time increasing in height to eight hundred or one thousand feet. The boulders on the beach change their character considerably about this place. Farther up, the yellowish-white limestone which occurs in Slave Lake formed a great portion of them; but here a greenish-gray, and rather dark-coloured, compact limestone, with a flat conchoidal fracture, replaces it. Variegated-sandstone, and some purplish, felspathose-sandstone, or compact felspar, also occur pretty frequently, together with slaty limestone, bituminous-shale, lydian-stone, pitchstone-porphyry, and various sienites, granites, and greenstones, almost all porphyritic.

The Rock by the river's side presents the first solid strata that occur on the immediate banks of the river after pa.s.sing the Forks. It is a round bluff hill about five hundred feet high, with a short obtuse-conical summit. A precipice three hundred feet high, washed by the river, is composed of strata of limestone, dipping N.W. by W. at an angle of 70 degrees; but the strata in other parts of the hill have in appearance the saddle-formed arrangement. [Sidenote: 127] The limestone is of a blackish-gray colour, slightly crystalline structure, and much resembles the stone of the princ.i.p.al beds in the hills at the rapid and mouth of Bear Lake River. Its beds are from one to two feet thick, and much intersected by small veins of calc-spar. There are also some larger veins a foot and a half thick, which traverse the strata obliquely, having their sides lined with calc-spar, and their centres filled with transparent gypsum. [Sidenote: 128] I observed a small imbedded pebble of white sandstone in the gypsum. [Sidenote: 127] Some of the beds of limestone consist of angular distinct concretions. [Sidenotes: 131, 132]

A small island lying off this rock, having its strata dipping south at an angle of 20 degrees, presents a bed a foot thick, entirely composed of these angular concretions, covered by a thin-slaty limestone, and reposing on thicker beds, all of which are dark-coloured. No organic remains were observed.

A few miles below the "Rock by the river side," a very rugged ridge appears on the eastern bank. It has sharp craggy summits, and is about five or six hundred feet high. For nearly sixty miles below this place the river continues about eight hundred yards wide, bounded by banks chiefly of clay; but in some places of a clayey shale having a bluish colour. The banks are in many places one hundred and fifty feet high, with a beach beneath covered with boulders. A little above the site of the Old Fort Norman the river dilates, and is full of islands; and a short way inland, on the east side, stands Clark's Hill, which is visible from Fort Franklin, and is supposed to be near 1500 feet high.

It is shaped somewhat like the amphibolic-granite mountain of Criffel in Galloway, and in its immediate neighbourhood there are some less lofty, but very rugged and precipitous hills, resembling in outline the ridges of limestone on Bear Lake River. From this place to the commencement of the lignite formation, already described, the banks of the Mackenzie are high and clayey.

MACKENZIE RIVER FROM BEAR LAKE RIVER TO THE NARROWS.

Below Bear Lake River the general course of the Mackenzie for eighty miles is about N.W. by W., when a remarkable rapid is produced by ledges of stone which cross its channel. The width of the river varies in this distance from one to three miles, but the water-course is narrowed by numerous islands, and the current continues strong. The Rocky Mountains are visible, running in a direction from S.E. to N.W. Judging merely by the eye, we did not estimate their alt.i.tude above four thousand feet, and I may remark, that the snow disappears from their summits early in the summer. A back view of the hill at the mouth of Bear Lake River is also obtained for upwards of twenty miles, but the ridge of which it forms a part curves inland, probably uniting, as was formerly remarked, with the one which crosses Bear Lake River near the middle of its course. The banks of the Mackenzie are in general from one hundred and twenty to one hundred and fifty feet high in this part, and there are occasional sections of them, but we had little leisure to examine their structure. In the voyage of 1826 we drifted down the stream night and day, landing only when necessary to cook our provisions; and in the following geological notices, as far as the pa.s.sage of the river named the _Narrows_, I have done little more than describe the specimens collected by Captain Franklin, when he ascended the river by the tow-line in 1825. The few notes that the rapidity of our voyage permitted me to make, as to the direction of the strata, &c., were inserted in the book that was purloined by the Esquimaux at the mouth of the river.

About fifty miles below Bear Lake River there is an almost precipitous cliff of bituminous-shale, one hundred and twenty feet high, strongly resembling the cliffs which occur near the bases of the hill of Scented-Gra.s.s and Great Bear Mountain in Bear Lake already described[34], and at the mouth of the Clear Water River in lat. 56-1/2 degrees. In the two former localities the shale is in the neighbourhood of horizontal strata of limestone; and in the latter it actually reposes on the limestone, which extends in horizontal strata as far as Great Slave Lake, is connected with many salt springs, and possesses many of the characters ascribed to the zechstein formation. [Sidenote: 133]

Captain Franklin observed the beach under the shale cliffs of the Mackenzie to be strewed not only with fragments of the shale, but also with much lignite, similar to that which occurs at the mouth of the Bear Lake River. Twelve or fourteen miles below these cliffs there is a reach seventeen or eighteen miles long, bounded by walls of sandstone in horizontal beds. [Sidenotes: 134, 135] Specimens obtained by Captain Franklin at the upper end of the reach consist of fine-grained quartzose sandstone[35] of a gray colour, and having a clayey basis, resembling those which occur in the middle of Bear Lake River. At the commencement of the "Great Rapid of the Mackenzie" there is a hill on each side of the river, named by Captain Franklin the eastern[36] and Western mountains of the Rapid. The Rocky Mountains appear at no great distance from this place, running about N.W. by W., until lost to the sight; and as the Mackenzie for forty or fifty miles below, winds away to the northward, and, in some reaches, a little to the eastward, they are not again visible, until the river has made a bend to the westward, and emerges from the defile termed "the Narrows."

The "Eastern mountain of the rapid" seems to have a similar structure, with the "Hill by the River's side," the hill at the mouth of Bear Lake River, and the other limestone ridges which traverse this part of the country. [Sidenote: 136] From some highly inclined beds near its base I broke off specimens of a limestone, having an imperfectly crystalline structure, and a brown colour, which deepens into dull black on the surfaces of its natural seams. [Sidenotes: 137, 138, 139, 141] A piece of dark-gray, compact limestone, having the peculiar structure to which the name of "_cone in cone_" has been given, was found on the beach; also several pieces of chert, and some fragments of a trap-rock, consisting of pieces of greenstone, more or less iron-shot, cemented by calc-spar.

Immediately below the rapid there are horizontal layers of sandstone which form cliffs, and also the bed of the river. Captain Franklin obtained specimens of this stone, which do not differ from the sandstones above the rapid. [Sidenote 142, 143, 140] And amongst the debris of the cliff he found other specimens of the "_cone in cone_,"

such as it occurs in the clayey beds of the coal measures, and also some pieces of crystallized pyrites.

[Sidenote: 144, 144a, 145, 146, 147, 144b] About forty miles below the rapid, the river flows through a narrow defile formed by the approach of two lofty banks of limestone in highly-inclined strata, above which there is a dilatation of the river, bounded by the walls of sandstone, which have weathered, in many places, into pillars, castellated forms, caves, &c. The sandstone strata are horizontal, have slate-clay partings, and seams of a poor clay-iron stone, but do not differ in general appearance from the sandstone beds at the rapid, except that a marly stone containing corallines, and having the general colour and aspect of the sandstone beds, is a.s.sociated with them at this place.

The very remarkable defile, below these sandstone beds, is designated "the _second rapid_" by Sir Alexander Mackenzie, and "the _ramparts_" by the traders, a name adopted by Captain Franklin. Mackenzie states it to be three hundred yards wide, three miles long, and to have fifty fathoms depth of water. If he is correct in his soundings, its bed is probably two hundred and fifty feet below the level of the sea. The walls of the defile rise from eighty to one hundred and fifty feet above the river, and the strata are inclined to the W.N.W., at an angle of seventy or eighty degrees. It is worthy of remark, that the course of the river through this chasm is E.N.E., and that just above the eastern mountain of the rapid it runs about W.S.W. through the sandstone strata, as if it had found natural rents by which to make its escape through the ridge of hills which cross its course here. Similar elbows occur in various parts of the River, and they may be almost always traced to some peculiarity in the disposition of the hills which traverse the country.

Captain Franklin gathered many specimens of the limestone strata of the Ramparts, which are specified in a note.[37] [Sidenote: 148, 149] Some of the beds at the upper part of the Ramparts consist of a granular foliated limestone, which was not noticed elsewhere on the banks of the river, but the greater part are of limestone, strongly resembling that which has been already described, as forming the ridges in this quarter.

Most of the beds are impregnated wholly, or in patches, with bitumen.