44 



MEXICO, CENTEAL AMEEICA, WEST INDIES. 



to the slight rainfall and long droughts, during which the springs run dry and 

 large rivers become impoverished, though their sources lie far inland on the interior 

 of the plateau, and like the Rio Yaqui even on the eastern slope of the Sierra 

 Madre. Many noisy torrents rushing through foaming cascades over the heights 

 of the Sierra Madre fail to reach the sea, and run out in the sands of the lowland 

 plains. Others, especially in Lower California, are mere wadies which are seldom 

 flooded, and their stony beds are the only roads in the country. To obtain a little 

 water oozing up between the shingle deep holes have to be sunk, which are locally 

 known by the name of bataques. The old estuaries have become salt pans, and the 

 Rio Colorado, whose lower course alone is comprised within Mexican territory, 

 resembles the rivers of Sonora in the slight amount of its discharge compared with 



Fig. 22. —Closed Basins of Mexico. 

 Scale 1 : 30,000,000. 



II3°40 



Wpst or GreenwicK 



89°40- 



i V 



Lakes of the closed bjsins. 

 ^^— ^— ^^^— ^— 620 Miles. 



the vast extent of its drainage area ; however, this great watercourse is navigable 

 for some hundred miles beyond the limits of the common frontier. 



All that part of Mexico which is comprised between the two converging 

 border ranges is also too arid for all its watercourses to unite in perennial streams 

 and reach the ocean through the Rio Bravo or any other large river. Most of 

 them, being too feeble to surmount the heights enclosing or intersecting the plains, 

 lose their waters in some shallow lagoon which rises or falls with the seasons. All 

 the saline basins met in Chihuahua and Coahuila are depressions of this sort formed 

 by torrents descending from the mountains. 



Such is the large Guzman lagoon near the Arizona frontier, where is discharged 

 the exhausted current of the Rio Casas Grandes at a lower altitude than the level 



