24 ORIGIN OF CAVE LIFE. 



masses of rocks fall in, which interrupt the passage below. Caves, 

 however, exist when the strata are horizontal. Their course is 

 changed by joints or faults, into which the excavating waters have 

 found their way. 



That these caves were formed prior to the postpliocene fauna is 

 evident from the fact that they contain its remains. That they 

 Were not in existence prior to the drift is probable, from the fact 

 that they contain no remains of life of any earlier period so far as 

 known, though in only two cases, in Virginia and Pennsylvania, 

 have they been examined to the bottom. No agency is at hand to 

 account for their excavation, comparable in potency and efficiency 

 to the floods supposed to have marked the close of the glacial 

 period, and which Prof. Dana ascribes to the Cham plain epoch. 

 An extraordinary number of rapidly flowing waters must have 

 operated over a great part of the Southern States, some of them 

 at an elevation of fifteen hundred feet and over (perhaps two thou- 

 sand) above the present level of the sea. A cave in the Gap 

 Mountain, on the Kanawha river, which I explored for three miles, 

 has at least that elevation. 



That a territory experiencing such conditions was suitable for 

 the occupation of such a fauna as the deposits contained in these 

 caves reveal, is not probable.. The material in which the bones 

 occur in the south is an impure limestone, being mixed with and 

 colored by the red soil which covers the surface of the ground. It 

 is rather soft but hardens on exposure to the air. 



The question then remains so far unanswered as to whether a 

 submergence occurred subsequent to the development of the post- 

 pliocene mammalian fauna. That some important change took 

 place is rendered probable by the fact, that nearly all the neotropi- 

 cal types of the animals have been banished from our territory, 

 and the greater part of the species of all types have become ex- 

 tinct. Two facts have come under my observation which indicate 

 a subsequent submergence. A series of caves or portions of a 

 single cave once existing on the southeast side of a range of low 

 hills among the Alleghany mountains in Wythe Co., Virginia, was 

 found to have been removed by denudation, fragments of the bot- 

 tom deposit only remaining in fissures and concavities,, separated 

 by various intervals from each other. These fragments yielded the 

 remains of twenty species of postpliocene mammalia.* This de- 

 nudation can be ascribed to local causes, following a subsidence 

 of uncertain extent. In a cave examined in Tennessee the Qssife- 

 rous deposit was in part attached to the roof of the chamber. 

 Identical fossils were taken from the floor. This might, however, 

 be accounted for on local grounds. The islands of the eastern 

 part of the West Indies appear to have been separated by submer- 

 gence of larger areas, at the close of the period during which they 



*See Proceed. Amer. Phil. Soc. 1869, 171. 



