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THE JOURNAL OF GEOLOGY.

were, I think, more favorable for rapid deposition than in the deep open ocean, but probably not as favorable as about coral reefs and islands. The limestones, and often the contained fossils, clearly indicate the presence of many of the same conditions of deposition as described by the authors I have quoted. More or less decomposed shells occur in nearly every limestone and a large proportion of limestone; especially the non-metamorphic marbles clearly show that they were deposited under the influence of the agencies at work in the laboratory of the sea. Willis states that this occurs in the shallow waters of the Everglades of Florida, and there is no a priori reason why it did not occur throughout geologic time,—on the contrary, there is no doubt that it did.

Rate of deposit in former times.—It has frequently been assumed that in the earlier epochs the conditions were more favorable for rapid denudation, and in consequence thereof the transportation and deposition of sediment was greater. Professor Prestwich considers^[1] that prior to the sedimentary rocks the land surface consisted of crystalline or igneous rocks subject to rapid decomposition owing to the composition of the atmosphere and to their inherent tendency to decay. They must have yielded to wear and removal with a facility unknown amongst mechanically formed and detrital strata where erosion operates. He thus accounts for one of the factors that gave the large dimensions and thicknesses of the earlier formations. Mr. Wallace thinks that geological change was probably greater in very remote time,^[2] stating that all tellurac action increases as we go back into the past time, and that all the forces that have brought about geological phenomena were greater.^[3]

↑ Geology, Vol. 1, 1886, pp. 60-61.
↑ Island Life, 2nd Ed., 1892, pp. 223-224.
↑ Sir William Thompson (Lord Kelvin), inferred from his investigations upon the cooling of the earth, that the general climate cannot be sensibly affected by conducted heat at any time more than 10,000 years after the commencement of the superficial solidification.Treatise on Natural Philosophy, Cambridge, 1883., Vol. 1, pt. 2, p. 478.Of the degree of the sun's heat we know so little that conjectures in relation to it have little force against the conditions indicated by the sedimentary rocks and their contained organic remains.

[1] Geology, Vol. 1, 1886, pp. 60-61.

[2] Island Life, 2nd Ed., 1892, pp. 223-224.

[3] Sir William Thompson (Lord Kelvin), inferred from his investigations upon the cooling of the earth, that the general climate cannot be sensibly affected by conducted heat at any time more than 10,000 years after the commencement of the superficial solidification.Treatise on Natural Philosophy, Cambridge, 1883., Vol. 1, pt. 2, p. 478.Of the degree of the sun's heat we know so little that conjectures in relation to it have little force against the conditions indicated by the sedimentary rocks and their contained organic remains.

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