CENTRAL AMERICAN GEOLOGICAL WATER WAYS. 591 



district is about four hundred and sixty feet above the sea, but it is 

 dissected by valleys such as that followed by the railway, whose 

 natural divide is two hundred and ninety-nine feet. It is only 

 reasonable to suspect that here may have been a former strait or 

 canal, but so far the terraces and gravel floors similar to those of 

 the Tehuantepec divide have not been described, as this is a feature 

 of only recent scientific inquiry. The interoceanic connections re- 

 ferred to by Dr. Maack belong to the older Tertiary period, preced- 

 ing the sculpturing of the physical features of the region, which were 

 long anterior to the water ways here described. 



Biological Evidence of Interoceanic Connections. — The 

 fishes, shells, sea urchins, and other organisms of the West Indian 

 basins belong to modern types, which to a large extent seem to have 

 migrated from the Atlantic Ocean. Their recent appearance sug- 

 gests great changes in the physical history of the West Indian seas, 

 which are only explicable on the theory of the Antillean bridge, as 

 set forth in the May number of this journal, and extended in the 

 present paper. For example, the West Indian region was a high con- 

 tinental mass with extensive plains where the sea basins now occur, 

 draining into the Pacific Ocean across the central part of America. 

 With the subsequent subsidence in the mid-Pleistocene epoch the 

 Antillean basins became seas, into which the modern Atlantic forms 

 of life gained access. The deep-sea fishes have absolutely no relation- 

 ship with those living in the Pacific Ocean, thus showing that the 

 American barrier obtained sufficient height for their exclusion; but 

 the littoral or shallow-water fishes and shells of the Pacific Ocean, to 

 a notable degree, are found in the West Indian waters. The term 

 deep-sea fauna here used applies to those forms living at greater 

 depths than from three hundred to five hundred feet, according to 

 circumstances. Thus it would appear that there were shallow water 

 connections with the Pacific Ocean in or since the mid-Pleistocene 

 epoch, such as have been shown from the study of the physical fea- 

 tures. But these water ways were either too small or of too short 

 duration for the general admission and commingling of Pacific and 

 Atlantic types. The modern characteristics of the deep-sea fishes 

 of the West Indian basins suggest that the older forms of Antillean 

 life had been expelled from the region, so as not to permit of the 

 development of their successors, as should have occurred if the con- 

 tinental area, now drowned, had not been generally drained. The 

 modern fades of the marine West Indian life thus supports the 

 physical evidence of a great Antillean continent or connection be- 

 tween N'orth and South America just prior to the introduction of 

 modern species. There is no inconsiderable degree of satisfaction to 

 the student in finding that the biological phenomena support the 



