THE WEST INDIAN BRIDGE. 25 



Indian region rose, and this time to its greatest height, so as to allow 

 the excavation of the very deep valleys and caiions through the then 

 existing table-lands which now form the submarine plateaus. Tliis^ 

 liigh elevation was characterized by such deep sculpturing as to give 

 rise to some of the boldest physical features of the lands with which 

 we are familiar. With the subsequent depression of the West 

 Indian bridge, the fragmentary islands became much smaller than 

 even now, and upper portions of the dro\\^led valleys were again 

 partly filled with a still newer formation (known as the Columbia of 

 the Southern States). This last has since been elevated a few hun- 

 dred feet, with some minor changes of level continuing to the present 

 day. The Columbia formation belongs to a mid-Pleistocene epoch. 

 Consequently, the time of greatest elevation and development of 

 the West Indian continent was during the early Pleistocene period — 

 more popularly called the Ice age. These great and recurring 

 changes of level of land and sea, in later geological times, have pro- 

 duced remarkable and startling revolutions in the physical geog- 

 raphy of the region, which might seem incredible but for the great 

 array of evidence which is now being accumulated on every hand. 



Relationship between the Distribution of Life and the 

 West Indian Continent.- — The elevation of the Antillean bridge is 

 a question of dynamical geology, but the consequent changes of the 

 physical geography naturally affected the distribution of life; ac- 

 cordingly, the biological aspect should be called upon as evidence of 

 the physical changes. 



The commingling of the littoral fauna of the Pacific Ocean with 

 that of the Antillean waters confirms the recent separation of the 

 two seas by the elevation of the Central American region. 



The character of the deep-sea fauna is very important. The 

 elevation of the West Indies to less than three thousand feet would 

 exclude the Atlantic waters from the Antillean seas, except through 

 two or three shallow straits, and one channel of enormous depth, be- 

 tween the Virgin Islands and St. Croix. According to the late Dr. 

 Brown Goode, the deep-sea fishes belong to modern forms, appar- 

 ently overflowing through the Caribbean Sea into the Gulf of 

 Mexico. There is no relationship whatever between the deep-sea 

 fishes of these basins and those of the adjacent waters of the Pacific 

 Ocean. The seemingly recent introduction of much the larger pro- 

 portion of deep-sea fishes from the Atlantic naturally indicates the 

 existence of barriers between the different basins — in other words, 

 an elevation of the region by a few thousand feet. Furthermore, 

 the general modern character of the fish fauna, with the exclusion 

 of the Pacific forms, suggests the inundation of the floors (including 

 possibly a few small sea basins) of the Caribbean and Honduras Seas 



VOL LIII — 3 



