which, I am informed, covers a considerable area. It consists, almost
entirely, of a compacted mass of spores and spore-cases. But the fine
particles of blown sand which are scattered through it, show that it
must have accumulated, subaërially, upon the surface of a soil covered
by a forest of cryptogamous plants, probably tree-ferns.

As regards this important point of the subaërial region of coal, I am
glad to find myself in entire accordance with Principal Dawson,
who bases his conclusions upon other, but no less forcible,
considerations. In a passage, which is the continuation of that
already cited, he writes:--

"(3) The microscopical structure and chemical composition of
the beds of cannel coal and earthy bitumen, and of the more
highly bituminous and carbonaeceous shale, show them to have
been of the nature of the fine vegetable mud which accumulates
in the ponds and shallow lakes of modern swamps. When such
fine vegetable sediment is mixed, as is often the case, with
clay, it becomes similar to the bituminous limestone and
calcareo-bituminous shales of the coal-measures. (4) A few of
the under-clays, which support beds of coal, are of the nature
of the vegetable mud above referred to; but the greater part
are argillo-arenaceous in composition, with little vegetable
matter, and bleached by the drainage from them of water
containing the products of vegetable decay. They are, in
short, loamy or clay soils, and must have been sufficiently
above water to admit of drainage. The absence of sulphurets,
and the occurrence of carbonate of iron in connection with
them, prove that, when they existed as soils, rain-water, and
not sea-water, percolated them. (5) The coal and the fossil