Page:A Treatise on Geology, volume 1.djvu/154

 138 induced since their aggregation, predominating over the yet traceable surfaces of deposition. This is sometimes expressed by the convenient though somewhat unlearned word, "slatified."

The nodular uneven surface of the limestones of this system is so remarkable, as to be of great importance in reasoning on the circumstances concerned in their production. It is extremely difficult to resist the notion that in many instances the limestone has been collected by molecular attraction from a mingled mass of argillaceous and calcareous sediment, round corals, and other organic marine exuviæ. The great abundance of corals in these rocks (Aymestry, Dudley, Wenlock, &c.) leads further to the supposition of their being really formed, like a coral reef, in the present seas. If this were correct, the whole of the substance of the rock must be supposed to have been abstracted from sea-water, by that vital action which dissolves the strongest chemical aggregations, and fixes the unwilling elements in new combinations. The perfectly laminated or bedded structure of the rock requires, further, the admission that the materials were arranged in obedience to the fluctuations of water: this, which implies the removal and partial drifting of the corals and shells, is strongly confirmed by the worn and rounded forms of some corals (Aymestry), the unattached condition of almost all (Dudley), the broken and crushed condition of many. If, therefore, we must compare the origin of the Wenlock and Aymestry limestones to that of a modern coral island or group of islands, the Bermuda group, where vital action furnishes the substance, and oceanic currents determine

Lowest fossileferous strata. Old red system