14 CUBA AND PORTO KICO 



From a physiographic point of view all the islands are 

 the upward-projecting tops of a varied configuration which 

 has its greatest relief beneath the sea, and which is of no 

 less interest to the student of physiography than the great 

 irregularities of the land. The islands which form the 

 outer rampart of the Caribbean Sea rise from submerged 

 ridges. The Antilles, connected by submerged sills, none 

 of which exceeds five hundred fathoms, also project upward 

 from vast foundations beneath the water. These features 

 strongly suggest the fact that the islands as we see them 

 to-day were once much more extensive lands. 



The systematic exploration of these depths began in 

 1872 on the west side of Florida, under the direction of the 

 American officers attached to the Coast Survey. Howell, 

 Pourtales, Alexander Agassiz, Bartlett, Sigsbee, Baird, 

 and others have studied the bottoms. Not only have care- 

 ful soundings been everywhere taken in order to map out 

 the relief, but the most sensitive instruments have been 

 used to determine the varying temperature at different 

 depths, the course of the upper and lower currents, their 

 saline properties, thermometric deviation, and other fea- 

 tures. 



Special attention has also been paid to the marine fauna 

 down to the darkest recesses of the abyss, and many star- 

 tling discoveries have been made, which open marvelous 

 vistas into the past evolution of life on the globe. It was 

 formerly supposed that the marine fauna was confined to 

 the surface or shallow waters, and that the stillness of death 

 reigned in the gloomy recesses of the deep. But the dreclg- 

 ings of the Blake and other exploring vessels in depths 

 of over two thousand fathoms have already increased the 

 number of animal forms the crustacean, for instance 

 from twenty to one hundred and fifty species, grouped under 

 forty new genera. The deep waters are also found to be 

 extremely rich in forms resembling the fossils of former 

 geological epochs, and to comprise numerous phosphores- 

 cent species. In certain places the marine bed is covered 



