ake 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 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