Having noticed the general features of this portion of the river, I have next to state, that the formation constituting 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. 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 48lustre. A frequent form of the lignite is that of slate, of a dull, brownish-black colour, but yielding a shining 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 passed 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.
81The 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 passes, 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 associated 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 quantity 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°, and, in his second journey, on the Peace River, in lat. 56° and 146° W. long.;" and further, that "the same was observed by Mr. Fidler, on the south branch of the Saskatchewan, in lat. 52° long. 112½° 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 Rivière la biche, 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 shining, thick lumps, which break, as he expresses it, like Spanish liquorice. It lies over beds of bluish-gray sandstone, and is associated with a white clay, which froths in water and adheres to the fingers.