PORTO RICO EXPERIMENT STATION. 385 



occurs a considerable area of level land, now devoted to the growing 

 of sugar cane. This, however, is supposed to have been a coastal 

 lagoon or lake, which became filled with sediment and was brought to 

 its present elevation (about 250 feet) and position by the uplifting of 

 the island. 



The mountains, while rugged, scarcely ever exceed 3,000 feet in ele- 

 vation. No topographic survey has ever been made of the island, 

 though one is much needed, and, consequently, reliable data as to 

 elevations are wanting. The highest eminence is attained on El Yun- 

 que, in the northeast part of the island. Spanish maps give this 

 mountain an elevation of 4,087 feet, but other authorities give it as 

 much less, the minimum being 3,200 feet. These mountains may be 

 considered nothing more than the peaks of a part of a great mountain 

 chain, which, if wholly emerged, would exceed in elevation any moun- 

 tains on the North American continent. To the north the shore of 

 the island drops off rapidly, and within less than 75 miles the water 

 attains a depth of 4,600 fathoms, or more than 5 miles. 



The elevations of Porto Rico are not sufficient to cause any marked 

 change in temperature, but owing to the prevailing direction of the 

 winds they have a marked effect on the distribution of the rainfall. 

 The combined influence of soil, rainfall, and elevation, however, has a 

 marked effect upon the character of the vegetation and makes clima- 

 tology a subject of vast importance. 



SOILS. 



The soils vary much both in formation and texture. About the 

 shore occurs a narrow fringe of coarse coral sand, which results chiefly 

 from the breaking down of the coral growth that is continuously in 

 process in the waters near the shore. This soil, with its accompany- 

 ing salt-water climate, is adapted to a comparatively limited flora, which 

 is quite distinct from that of the interior. Here the cocoanut palm, 

 yarey palm, and the sea grape find a congenial home, and the soil 

 seems well adapted to the growing of pineapples. Bordering this to 

 the landward are two types of soil, viz, the mangrove swamps and the 

 playa plains. The former are swamp areas, which are about midway 

 between high and low tide in elevation and are, therefore, inundated 

 to the depth of about a foot by every rise of tide. The soil is often 

 made up of a mixture of the coral sand and the finer material which is 

 brought down from the interior, together with much organic matter 

 resulting from the decay of the falling leaves of the mangrove bushes, 

 which gives to the soil a black color. The soil is necessarily charged 

 with salt and has no economic value except for the purpose of future 

 reclamation by diking and pumping. 



The soils of the playa plains, owing to the sources of their origin, 

 vary much in character. They are all alluvial, however, and brought 

 H. Doc. 334 25 



