450 Dr. J. W. Spencer — The Antillean Continent. 



was a high plateau as is Mexico and the Great Basin to-day. 

 This was the first period of the formation of the great canons, and 

 the modern topographic features. But at the close of the Pliocene 

 period there was a submergence of from 100 to 1300 feet below 

 the present altitudes, with the deposition of from 100 to 260 feet of 

 (Matanzas) limestones. During this epoch the connections with 

 the Pacific Ocean were shallow. 



The earlier Pleistocene days were characterized by a re-elevation 

 of the continent with great erosion and the clearing out and 

 extension of the older Pliocene valleys. The continental develop- 

 ment was nearly the same as in the earlier Pliocene continental 

 epoch. 



In Mid-Pleistocene times the continent was again depressed, so 

 that the West Indian islands were reduced to a much smaller size 

 than at present, but not so small as during the subsidence at the 

 close of the Pliocene days. These later deposits were mostly loams 

 and gravels. Some minor oscillations are recorded in the terraces. 



Again there was a slight elevation of from 100 to 300 feet as 

 shown in the canons which form the outlets of many harbours. 

 Then followed the depressions that gave rise to the latest terraces, 

 which have been recently elevated, as also the modern coral reefs. 

 Some portions of the region seem to be sinking very slowly and 

 others rising. 



In the Miocene period there was free communication between 

 the Atlantic and Pacific Oceans. This was cut off by the Pliocene 

 continental elevation, but slightly reopened in the later Pliocene 

 submergence. Again the Atlantic waters were driveij back in the 

 earlier part of the Pleistocene period, after which the later depression 

 freely admitted the Atlantic waters, with probably a shallow con- 

 nection with the Pacific Ocean for a short time. Since the Mid- 

 Pleistocene epoch the gentle undulations have made no changes in 

 the sea connections, but have only varied the breadth of the now 

 slightly submerged coastal plains. 



The physical changes appear to explain the occurrence of the 

 greater number of the marine fauna of the Antillean region. In 

 this abstract the Sea of Honduras has not been explained, but it 

 may have been a basin from earlier times than the date of the Gulf 

 and Caribbean basins. The physical history is in accord with the 

 distribution of mammals. The late Miocene fauna of Florida could 

 not have reached the islands, and in that region there is no known 

 Pliocene fauna to be considered even on the adjacent parts of the 

 northern continent. At the close of the Pliocene period the lands 

 were reduced to a few very small islets, and the coastal plain of the 

 continent was submerged. Then followed the continental rise with 

 a rich Pleistocene fauna in Florida, and some forms are known in 

 the islands, but their life was again cut off by the next subsidence, 

 since which time the modern types of mammalian life of Florida 

 have not been able to reach the islands. In short, the physical 

 history seems to explain the disappearance of many mammals from 

 the region, for with a continental change of altitude of from 8000 to 



