INTRODUCTION ivi 
The lowlands on the Pacific side of our area form a 
narrow fringe which becomes more valuable for agri- 
cultural purposes as we proceed towards the south. 
The lowlands of the Atlantic side are of varying widths. 
The greatest land mass of uniformly low elevation is 
-the Peninsula of Yucatan. In eastern Honduras and 
Nicaragua there are extensive river valleys of low ele- 
vation. 
The river systems of Mexico and Central America 
flow into the two bounding oceans or into lakes which 
have no outlets. Several closed basins occur on the 
Mexican table-land. The Rio Nazas and the Rio 
Nieves flow into salt marshes in the northern state of 
Coahuila. But the most important interior basin is 
the Valley of Mexico. In this mountain enclosed val- 
ley, whose general level is 7,500 feet above the sea, there 
are five lakes which in order from north to south are 
named Tzompanco, Xaltocan, Tezcoco, Xochimilco, and 
Chalco. The last two contain fresh water, since they 
drain into Lake Tezcoco, but the rest are more or less 
brackish. Lake Tezcoco is by far the largest although 
its area has been greatly reduced by natural and artifi- 
cial causes since the coming of the Spaniards. 
The largest river of Mexico is the Rio Lerma which 
takes the name Rio de Santiago during its deep and 
tortuous passage from Lake Chapala to the Pacific. 
Farther to the south is the Rio de las Balsas which like- 
wise flows into the western ocean. The name means 
“River of the Rafts” and is given because of a peculiar 
floating apparatus made of gourds tied to a wooden 
framework that is used on this stream. Flowing into 
the Gulf of Mexico are several large streams, among 
which may be mentioned the Panuco, Alvarado, 
Grijalva, and Usumacinta. The last is by far the great- 
est in volume of water, and with its maze of tributaries 
