BERKEY, GEOLOGICAL RECONXOISSANGE OF FORTO RICO 3 



ceptable manner. !Most of the writiags- of this kind are widely scattered 

 in Yolmnes of periodicals or proceedings of learned societies or pamphlets 

 which in most cases are not readily obtained or consulted. 



From a perusal of these articles^ one learns that Porto Eico belongs 

 structurally and genetically to the mountain chain now represented by 

 the isolated islands forming the principal West Indian group. Enough 

 work has been done^ especially by E. T. Hill,^ to outline roughly the 

 geological history of the Island of Porto Eico and indicate on a map the 

 distribution of some of the formations. An especially good general de- 

 scription of ph3'sical features^ alsO;, is given b}'' H. M. AYilson."* An intro- 

 ductory general description, in large part along the same lines as these, 

 will probably serve the present purpose. 



General Description 



The Island of Porto Eico is situated in the Torrid Zone between lati- 

 tude 17° 54" and 18° 30'' north and longitude 65° 13'' and 67° 15" west. 

 It is the easternmost and southernmost of the Greater Antilles. It lies 

 within the trade-wind belt, and the constancy of these winds gives the 

 island a remarkably mild and uniform climate. There is an abundance 

 of rainfall on the windward side, which in this case is the east end and 

 the north side as far west as Camu}-. The effect of the mountains across 

 which these winds blow is to make the south side of the island and most 

 of the western portion comparatively arid. Some districts are said to 

 have no rainfall for a whole year at a stretch. 



The Atlantic Ocean lies to the north and east, the Caribbean Sea lies 

 to the south, while Mona Channel on the west separates the Island of 

 Porto Eico from IIa}d:i. BroT\Tison Deep, reaching the profound depth of 

 twenty-four thousand feet below sea level, one of the deepest spots known, 

 lies immediately to the north. Tanner Deep lies to the south, reaching 

 a depth of fifteen thousand feet. Although the relief of the island above 

 sea level is less than four thousand feet, this represents only the extreme 

 top of a great mountain mass which rises above the submerged platform, 

 from which its real height should be measured. The extreme relief differ- 

 ence represented by the summit of El Yunque on the one hand and Brown- 



2 The writings referred to, together with others that have some description of physical 

 conditions in Porto Rico, are listed at the end of this paper. Those of most usefulness 

 in the present investigation are certain papers by R. T. Hill and H. M. Wilson, besides a 

 very few others of less extended character. 



3 R, T. Hill : "Porto Rico." National Geographic Magazine, volume 10, pages 93 to 

 112 (1889). 



* H. M. WiLSOX : "Water Resources of Porto Rico." Water Supply Paper No. 39, 

 U. S. Geological Survey. 



