he eddies,
form shoals, which ultimately augment into islands. A thicket of small
willows covers the new-formed island as soon as it appears above water,
and their fibrous roots serve to bind the whole firmly together.
Sections of these islands are annually made by the river, assisted by
the frost; and it is interesting to study the diversity of appearances
they present, according to their different ages. The trunks of the trees
gradually decay until they are converted into a blackish brown substance
resembling peat, but which still retains more or less of the fibrous
structure of the wood; and layers of this often alternate with layers of
clay and sand, the whole being penetrated, to the depth of four or five
yards or more, by the long fibrous roots of the willows. A deposition of
this kind, with the aid of a little infiltration of bituminous matter,
would produce an excellent imitation of coal, with vegetable impressions
of the willow-roots. What appeared most remarkable was the horizontal
slaty structure that the old alluvial banks presented, or the _regular
curve_ that the strata assumed from unequal subsidence.

"It was in the rivers only that we could observe sections of these
deposits; but the same operation goes on, on a much more magnificent
scale, in the lakes. A shoal of many miles in extent is formed on the
south side of Athabasca Lake, by the drift-timber and vegetable debris
brought down by the Elk River; and the Slave Lake itself must in process
of time be filled up by matters daily conveyed into it from Slave River.
Vast quantities of drift-timber are buried under the sand at the mouth
of the river, and enormous piles of it are accumulated on the shores of
every part of the lake."[1062]

The banks of the Mackenzie display almost everywhere horizontal beds of
wood coal, alternating with bituminous clay, gravel, sand, and friable
sandstone; sections, in short, of such deposits as are now evidently
forming at the bottom of the lakes which it traverses.

Notwithstanding the vast forests intercepted by the lakes, a still
greater mass of drift-wood is found where the Mackenzie reaches the sea,
in a latitude where no wood grows at present except a few stunted
willows. At the mouths of the river the alluvial matter has formed a
barrier of islands and shoals, where we may expect a great formation of
coal at some distant period.

The abundance of floating timber on the Mackenzie is owing, as Dr.
Richardson inf