658 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 fos- 

 sils, 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 influ- 

 ence 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 through- 

 out 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 favor- 

 able for rapid denudation, and in consequence thereof the trans- 

 portation and deposition of sediment was greater. Professor 

 Prestwich considers x 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 

 times, 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. 



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. 



