384 REPORT OF OFFICE OF EXPERIMENT STATIONS. 



is about 1,400 miles, while the distance to New Orleans is slightly 

 greater. 



In form the island is a parallelogram, with its long axis extending 

 almost due east and west. In extent it is 36 miles wide by 100 miles 

 long, embracing an area of 3,600 square miles. 



CONFIGURATION. 



The topography of the island consists chiefly of interior mountains 

 and coast border plains, the latter representing only about one-tenth 

 of the whole. The formation of the island is volcanic, the rocks con- 

 sisting principally of limestones, together with small amounts of 

 granite, marble, sandstone, and serpentine. The limestone varies 

 greatly in its character and hardness. In the interior it is usually of 

 a blue or grayish crystalline nature, and well adapted for burning into 

 lime, although but little used for this purpose. The surface of these 

 rocks is almost entirely disintegrated, forming a soil several feet in 

 depth, which gives to the mountains a smooth appearance and fur- 

 nishes a good footing for vegetation. Along the marginal foothills 

 the limestone is of a white and chalky appearance, and is sponge-like 

 in texture. It is usually spoken of as coral limestone, and the cavities 

 often contain seashells. This coral limestone gives rise to foothills, 

 having very steep acclivities, and terminating in very sharp and 

 jagged points. The rocks are more exposed than in the interior, but 

 their porous nature f urnishes^a good footing for plants, and the hills 

 are usually covered to their summits with verdure. These rocks are 

 much used in the construction of roads. 



The main backbone of the island extends almost due east and west 

 and is fully two-thirds of the distance to the south side. The water- 

 shed of the north is therefore twice as extensive as that of the south, 

 and because of the greater rainfall on the former, the rivers are more 

 than correspondingly larger. 



The coastal plain consists chiefly of level stretches of alluvial land 

 which in places takes on an undulating aspect. In a number of places 

 this coastal plain is broken by the mountains coming directly to 

 the seashore. It rarely extends inland more than 5 miles and the 

 greatest breadth usually occurs at the mouth of the larger rivers. 



The interior mountain country is cut by numerous streams which 

 ramify in every direction and give rise to deep but very narrow val- 

 leys. The river bottom lands are in small irregular areas which occur 

 first on one side of the stream and then on the other as it sweeps the 

 valley from side to side in its course to the sea. In many places no 

 bottom lands are present, the valley being so narrow that it is occupied 

 only by the rocky bed of the river. 



In a few instances the valleys widen out into a considerable area of 

 bottom lands. The most noted example of this is at Caguas, where 



