1848. GRAVEL BEDS. 189 were on fire near Bear River, when Sir Alexander Mackenzie discovered them, in 1785, and the smoke, with flame visible by night, has been present in some part or other of the formation ever since. From one to four beds of coal are exposed above the water level on the banks of the river, the thickest of which exceeds three yards, and was visible a short way above Bear River in the autumn only,—the Mackenzie being then seven or eight feet below its spring level. Interstratified with the coal beds, there are layers of gravel which occasionally, through the intermixture of clay more or less iron-shot, acquire tenacity enough to form vertical cliffs, but more often are very crumbly. The pebbles composing the gravel vary in size from that of a pea to that of an orange, and are formed of Lydian-stone, flinty slate, white quartz, quartzose sandstone and conglomerate, clay-stone, and slate-clay. The gravel is sometimes seamed by thin layers of fine sand, and its beds vary in thickness up to thirty or forty feet. In place of the gravel, a friable sandstone is often interposed between the coal beds or rests upon them. It is fine-grained, often dark from the dissemination of bituminous matter, and has so little tenacity, that in many places it is excavated by the sand-martens. Being porous, it fills with water, and is frozen into a compact, hard rock, for most of the year; but becomes moist, and breaks down under the influence of the hot rays of the sun in spring. Potter's clay, of a grey or brown colour, alternates with the beds already named, in layers varying from one foot to forty or more in thickness. This clay is often highly bituminous, and is penetrated by ramifications of carbonaceous matter, resembling the roots of vegetables. About ten miles above Great Bear River, a layer of this material, lying immediately over a bed of coal which was on fire, has been baked so as to resemble a fine yellowish-coloured biscuit porcelain. In a part of this, I found numerous impressions of leaves, most of them dicotyledonous, but one of them apparently coniferous, and belonging, probably, to the yew genus. The existence on many of the leaves of the latter plant of little round bodies like the fructification of ferns, invested the specimens with much interest: and I am indebted to Mr. Brown for examining them, and superintending the accurate drawings, made by Mr. Sowerby, junior, from which the accompanying plates have been engraved. The clay had unfortunately cracked so much under the influence of the heat to which it had been subjected, that I could not obtain entire specimens of the larger dicotyledonous leaves, 1848. EDIBLE CLAY. 191 but in the general character of their venation they resemble the Acerineæ. Some portions of the clay was semi-vitrified, and so hard as to receive no impression from a file; and I gathered pieces of this kind, composed of blue semi-vitrified layers, alternating with others of a rich buff colour. All the indurated clay, containing leaves, splits easily into thin layers, in every one of which there were impressions, so that the various kinds of leaves must have been deposited thickly above one another at this place. The fossiliferous clay is covered by one hundred and forty feet of sand and sandstone, and by some thin layers of conglomerate. A pipe-clay is very generally associated with the coal beds, and is frequently found in contact with the lignite. It exists in beds varying in thickness from six inches to a foot, and is generally of a yellowish-white colour, but in some places has a light lake-red tint. It is smooth, without grittiness, and when masticated has a flavour somewhat like the kernel of a hazel nut. When newly dug from its bed, it is plastic, but in drying becomes rather meagre and adheres to the tongue: its streak is less glistening than that of ordinary English pipeclay. As the natives eat this earth in times of scarcity, and suppose that thereby they prolong their lives, I requested Dr. Davy and the late Dr. Prout to examine it, but neither of these able |