Precipitation

VI PL.

32 NO. PAPER WATER-SUPPLY

SURVEY GEOLOGICAL S. U.

FOREGROUND-. IN TREE ORANGE AND HOUSE PEASANT'S DIAZ; JUANA NEAR HILLS BARREN

are extensive alluvial playas similar to those already described, and highly cultivated in sugar cane.

The country traversed by the main highway from Mayaguez via San German and Yauco to Ponce has already been generally described as differing essentially in topographic characteristics from any of the other portions of the island passed over. The road skirts the south- western slopes of the main sierra. Between it and the sea, distant in some places as much as 8 to 10 miles, are a series of low, rolling lime- stone hills tilted upward toward the interior and separated by two extensive parting valleys. The erosive action which has produced the long valleys marking the junction line between the foothills which parallel the main mountains promises, according to Mr. B. T. Hill, to reduce these valleys to sea level in the near geologic future, and thus to cut off from Puerto Rico a small island including the country round about Cabo Rojo and Lajas.

From Mayaguez, through Hormigueros and San German, to Sabana Grande is a great valley, through which flows the Rio Guanajibo. It is this which separates the main summits from the rolling foothills to the south, which are hereby dignified by the collective name of Cerro Gordo. Between Sabana Grande and Yauca is a low divide con- necting the Cerro Gordo with the main sierra and separating the greater valley from a similar but smaller valley, which includes the lagoon of Guanica and extends from Guayanilla and Yauco to the port of Cabo Rojo. (PI. VIII, A.) Still south of the valley and sep- arating it from the Caribbean Sea is a second well-defined ridge of low limestone and coral hills.

CLIMATOLOGY.

Situated as the island is, with a middle latitude of about 18° 15' N., which is well within the torrid zone, it is seen to be in the same approximate latitude as the City of Mexico, the Hawaiian Islands, the Sahara Desert, and Bombay, India. Because it is the easternmost of the Great Antilles, however, its climate is so tempered by the trade winds as to render it more moist and salubrious than that of any of the regions named, with the possible exception of the Hawaiian Islands.

To the trade winds primarily, and to the influence upon them of the high mountain summits in the interior of the island, are to be ascribed the moderate temperature and the peculiar distribution of precipitation which characterize this island. Though smaller in area by 1,000 square miles than the State of Connecticut, its extremes are subject to as great difference in rainfall, both in amount and occur- rence, as are the extremes of the United States. The trade winds blow with unceasing regularity throughout the year, though not with such force as to be disagreeable. Their pressure is felt as wind move- ment but a short distance from the northern and eastern coastg, yet