Generally speaking, the conformation of the island is slightly undulating, with the exception of a mountain range which traverses it from east to west, running through nearly its whole length in a zig-zag course, and on the average about twenty-five miles distant from the north coast.
This range divides the island into two unequal portions. The largest is on the north, and the rivers flowing through that section are much the longer. A part of the main range is called Sierra Grande or Barros. The northeast spur is known as the Sierra de Luquillo and the northwest as the Sierra Larea. The general height of these mountains is about 1,500 feet above the sea, but there is one peak, Yunque, which reaches a height of 3,678 feet. This can be seen seventy miles at sea, and would be a magnificent place for a shore signal for the benefit of the ships that sail the South Atlantic seas.
It is noticeable that there are no extensive lakes in the highlands of the interior, but there are many interesting caves in the mountains, the principal ones being those of Aguas Buenos and Ciales.
The elevated ridge which crosses the island intercepts the northeast trade winds which blow from the Atlantic and deprives them of their moisture. The consequence of this is that the rainfall in the northern portion of the island is very copious. It also has the effect of reducing the rain south of the mountains, so that there is a prevalence of droughts in that section and agriculture can be advantageously carried on by irrigation. Up to the present, however, this work of irrigation has been very imperfect and unsystematic, and the results on the whole have not been satisfactory.
The Luquillo range ends ten miles from San Juan. The capital is, therefore, to a certain degree sheltered by a mountain wall from the rain-bearing winds, which, in the warmest months blow mainly from easterly points. Still all the northern adjacent shores and lowlands are subject to flooding by torrents of rain.
Taking it as a whole, the island is approximately roof-shaped, so that the rainfall is rapidly drained off.
In the interior are extensive plains and there are level tracts from five to ten miles wide on the coast.
The soil of Porto Rico is exceedingly fertile. In the mountains it is a red clay, colored with peroxide of iron, in the valleys it is black and less compact, and on the coasts it is sandy, but capable of some culture.
The pasture lands in the northern and eastern parts of the island are superior to any others in the West Indies.
Porto Rico is essentially a land of rivers and streams. Of course none of them are of any great length, but of the entire number, some thirteen hundred, forty are navigable for more or less distances for commercial purposes.