136 J. W. SPENCER — RECONSTRUCTION OF ANTlLLICAN CONTINENT. 



Still there are some common types even in Florida. Accordingly, what- 

 ever value there is in the distribution of the shells, there appears nothing- 

 unfavorable to the late continental connections set forth on dynamic 

 grounds, although in the great changes of altitude marked effects would 

 be produced upon the species ; yet at no time during the high continental 

 elevation was there an absence of low land in some locality of the central 

 continent. Today the bridge between Cuba and Yucatan for a length of 

 over a hundred miles has been swept away to a depth of 7,000 feet, while 

 that between the Bahamas and Florida is gone for a width of 43 miles 

 and a depth reaching to only 2,100 feet. 



As Dr Ball's assistance with regard to the invertebrate paleontology 

 has been invaluable to me, so I base my studies of the relation of the 

 mammals to the physical condition of the West Indies on the interpre- 

 tation of the fauna by Professor E. D. Cope, confirmed by Professor 

 W. B. Scott. 



After the esirlj Eocene marine fauna of the Zeuglodon type which 

 flourished on the southeastern coast the next mammalian forms known 

 are from the beds which Dr Dall has named the Alachua clays ^ (from 

 Archer and Mixon's Florida). The bones are thoroughly mixed up, so 

 that no two of the same individual are in juxtaposition. Some tremen- 

 dous disturbance has come over these graves. The clays occupy depres- 

 sions and ravines on the eroded surfaces of Eocene and Miocene strata^ 

 but they have been removed from the higher grounds, if ever there. 

 From these deposits Dr Leidy determined the following species : 



Rhinoceros (Aphelops) jproterus (Leidy). 



Mastodon floridanus (Leidy). 



Megatherium sp. 



Procamelus (^Pliauchenia) major (Leidy). 



Procamelus (Pliauchenia) minor (Leidy). 



Procamelus (Pliauchenia') minima (Leidy). 



Hippotherium ingenuum (Leidy). 



Hippotherium plicatile (Leidy). 



All of the species are identical or are closely related to the western 

 Loup Fork series according to Professors Cope and Scott ; consequently 

 they belong to the very latest Miocene or very earliest days of the Plio- 

 cene — in short, to a transition epoch. During that epoch the altitudes 

 of the southeastern parts of the continent were much the same as the 

 present, and it was not connected with the West Indies, which were all 

 submerged except a few small islets. No true Pliocene mammals are 

 known east of the Mississippi river (Cope) ; consequently we are ignorant 

 of a mammalian fauna on the northern continent, without much expecta- 



* Bull. U. S. Geol. Surv., no. 84, by Dr W. H. Dall, pp. 129, 130. 



