34 Professor Silencer — Continental Elevation. 



original paper upon the submarine river-like valleys was prepared, 

 but they now greatly strengthen the inferences that the drowned 

 plateaux may be used as " yardsticks " for measuring the amount 

 of late continental elevation. 



In his paper referred to, Professor Hull endorses the correctness 

 of the interpretation that the submerged valleys were formed by 

 atmospheric agents. Such inferences being correct, the West Indies 

 formed a high continental plateau, while the Gulf of Mexico and 

 the Caribbean Sea were plains or inland lakes draining into the 

 Pacific Ocean across what are now low passes of Mexico and Central 

 America. 



Date of the Continental Elevation. 



Elsewhere the writer has shown ^ that the old Mio-Pliocene 

 surfaces extended much beyond their present limits, and were 

 subjected to long-continued reduction to base - levels of erosion. 

 Upon the undulations of the country then produced, the Lafayette 

 deposits of the continent form an extensive mantle, which has been 

 provisionally considered as belonging to the late Pliocene epoch. 

 The surfaces are enormously denuded. Following this formation 

 northward, although there are but few exposures of contact, the 

 writer has observed near Somerville, N.J., the Lafayette overlain 

 by a few feet of glacial drift, which has been extensively denuderl, 

 as it is locally wanting. Besting upon the boulder drift, and where 

 this has been removed, upon the underlying Lafayette loams and 

 gravels, the Columbia formation may be seen. This feature shows 

 that the epoch of glacial deposits occurred between the Lafayette 

 and Columbia periods. Consequently, the epoch of great elevation, 

 which favoured the excavation of the valleys, coincided with that 

 of the glacial deposits of the early Pleistocene days. 



Migration of Mammals. 



The Antillean Continent formed a bridge connecting North and 

 South America, over which only a few mammalian remains have 

 been found, as the greater portion of it is now beneath the sea. At 

 Port Kennedy, Pennsylvania, an extensive fauna has been discovered 

 in fissures, and upon it Professor Edward D. Cope was engaged at 

 the time of his recent death, but some results he had made known. 

 Of 38 species of mammals, so far determined, a large percentage are 

 extinct, and among these occur Eqims and Megalonyx. There is 

 also an abundance of remains of an old form of South American 

 bear, which are not known to have crossed the plains of the West. 

 The occurrence of these types at Port Kennedy, Professor Cope 

 regarded as strongly supporting the theory of the Antillean bridge 

 in the early Pleistocene epoch. There is also a newer cave-fauna in 

 Eastern North America, which belonged to a later period, separated 

 from the first by a partial submergence, according to the conclusions 

 of that distinguished author. Elephas has recently been found in 

 Guadeloupe. 



1 " Reconstruction of the Antillean Continent," cited before. 



