DEFOKMATION OF THE WEST INDIAN KEGION. 121 



derived from localities now depressed beneath the sea or buried by later 

 accumulations ; so also from the Cretaceous days, or before, to modern 

 times great volcanic activit}^ in one locality or another has been added 

 to the geologic forces of the region of the West Indies. 



During the earlier i)art of the Eocene ])eriod a portion of the West In- 

 dies was elevated, but this elevation does not seem to have extended to 

 the adjacent continental area. During the later Eocene and most of the 

 Miocene period only a few islands appear to have existed in the seas 

 of the West Indies and Central America, and the accumulations of 

 strata reached extensive proportions. As the Miocene often succeed the 

 Eocene strata without a break, they form a physical unit. In Cuba their 

 united thickness, actually observed, is 1,400 feet, with a faulted structure, 

 which indicates a total development amounting to 2,000 feet. Along 

 Chattahoochee river the Eocene is 1,400 feet thick. At Jacksonville, 

 Florida, the upper Eocene, beneath 400 feet of overlying accumulations, 

 extends to a depth of 1,500 feet without reaching the bottom beds. At 

 Galveston 2.000 feet of upper Miocene (Dall) alone have been revealed 

 in a well. At Savannah Miocene strata have been denuded to a depth 

 of 250 feet below tide in the buried valley, and in southern Florida, be- 

 neath the late Pliocene basin, only four feet of upper Miocene strata re- 

 main (Dall), In Jamaica the Eocene and Miocene strata aggregate 5,000 

 feet (Sawkins), and there the deposits have been raised to 3,000 feet above 

 the sea.^ The Miocene formation of San Domingo is 2,000 feet thick and 

 raised to an altitude of 3,855 feet (Gabb). The greatest elevation of the 

 Miocene in Cuba appears to be 2,300 feet south of the Sierra Maestra.f 

 Similar limestones form the divide of the isthmus of Tehuantepec, and 

 on adjacent hills rise to 1,000 feet,:|: with the maximum height unknown. 

 At Panama the Miocene strata occur to a height of 500 feet on some hills 

 rising out of the harbor (Maack),§ and in the neighboring parts of Costa 

 Rica they rise to 3,000 feet (Gabb). Similar strata also form the divides 

 between the valley of, Atrato and the Pacific ocean, with elevations of 7G3 

 feet and higher, l)ut the maximum elevation is not given. Thus in the 

 Miocene times, so far as can at [)resent be determined, only a few small 

 islands of Cretaceous, with some plutonic, rocks could have risen above 

 the common surface of the Atlantic and Pacific oceans, and all of the to- 

 pograj)hic and hydrographic features are post-Miocene. 



In the Miocene period there api)ears to have been a great subsidence of 

 many portions of the Antillean and continental regions. Along the coast 



♦See reports on J.imiiica and Sun Domingo, cited before, 

 t J. P. KimV)nll, Am. Jour. Sn., Dec, 1884. 



J Report on "Isthmus of Teliiiantepec,'* l)y J. d. 15 iriianl and J. J. Williams, Appleton'a, 1852 

 (Mee j<«"l*>Kic.'il section). 

 I '• Isthmus of D.irieu Ship Canal," U. S. Navy Department, 1874. 



