Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

ON THE DELUGE. 673 Still there are some points but lightly touched, or unnoticed, by any person whose works bearing particularly on this sub- ject I have yet seen. One is the rapidity with which certain substances combine under water, and form stone ; such, for instance,* as those used in Roman cement: — another is the possibility of fragile substances, such as shells, small creatures, leaves, corallines, branches, &c., being enveloped in a muddy matrix, while floating at various depths, according to their spe- cific gravities ; and the precipitation (chemically speaking) or consolidation, or simple deposition of such cohering masses.-f- The similarity of coal to asphalte inclines one to suspect an identity of origin ; and that coal, in a fluid state, enveloped quantities of vegetable matter — was for some time agitated by the continual tides and tidal currents of the diluvial ocean, and afterwards hardened by cooling, by pressure, or by chemical cheaige ; if not by all three. We find the impressions of leaves, stems, and branches — and even large woody trunks embedded in coal : but that the matrix, in which the leaves were enveloped and subjected to pressure, was not triturated vegetable matter is probable, because the casts of delicate vegetable substances found in it show few, if any, signs of friction or maceration. The impressions are as beautifully perfect as those of shells in fossils where the shell itself has disappeared. Might we not as well say that limestone was formed out of decomposed or pulverised shells, as assert that coal was formed out of the luxuriant herbage, the ferns and the palms, of a former state of the world ? Asphalte is at first buoyant; that trees and other vegetable productions are so I need not remark; but coal sinks in water, and asphalte may be altered chemically so as to sink like coal. Experiments on the asphalte of the famous lake at Trinidad have proved that there is so very close an analogy between that substance and coal, that a gas, exactly resembling coal gas, and • Lyell, Elements of Geology, 1838, p. 75-6. t The simplest experiments with pulverised, or numerous minute substances in water, shew that they attract one another mutually, and then cohere. VOL. II. 2 X