102 



PORTO RICO 



drifted sand— and then a sand}' beach, with the sea constantly breaking 

 over the jagged teeth of broken and sunken reefs, here and there close 

 into shore — a rocky rugged island, small and generally verdureless." 



The coast-border topography may be broadly conceived as a 

 narrow belt of low hills and plains encircling the main or moun- 

 tainous mass of the island, and broken in continuity upon the 

 northeast, southeast, and west by spurs of the central mountains 

 which run across it into the sea. This border region of itself is 

 an exceedingl y diversified area, presenting two conspicuous major 

 types of relief, coast hills, playa plains, and generally a third 

 type which may be called parting valleys. 



Seen from the sea the coast-border topography at the south- 

 west end presents the aspect of a low tilted bench or plain, 

 bluffing rather abruptly at the water's edge, and its summit 

 gently arching toward the foot of the ribbed and corrugated 

 front of the mountains. Here and there a stream from the 

 mountains cuts across this coast bench and severs it into blocks 

 of hills. These stream valleys are wide alluvial plains, fre- 

 quently of a much greater area than the hills. The hills result- 

 ing from the dissection of this bench may be either round or 

 oblong, according to the amount of erosion; but of whatever 

 shape their slopes are always regular and void of the strong 

 vertical corrugations and knife- edged salients which characterize 

 the mountains. They are also distinguished from the interior 

 mountains by their entirely different geologic composition, and 

 on the south coast by their vegetation. 



For want of a better word, the term " playa plains " may be used 

 for the wide alluvial plains which sever the coast bench into 



HILLS OF COAST BORDER, CAROLINA 



