The Isthmus of Tehuantepec. 



161 



height of seven hundred and forty-five and seven hundred 

 and thirty feet. 



These are called the passes of Tarifa and Chevilla. They 

 are about twenty-five miles apart, and from each of them 

 the slope is easy and gradual to the sea. Through one of 

 these the canal, or railroad, must be built, if ever built at 

 all. 



Between the table lands and the Pacific, are the Pacific 

 Plains. 



In the plains near the sea, are two large lagoons, or 

 lakes, containing, together, one thousand square miles. 

 These lakes have an interest related especially to the canal. 

 Their depth varies from one to twenty feet. The average 

 depth over half of their area is, probably, fifteen feet. 

 Seven rivers discharge into them. Both lakes discharge 

 into the sea, through an outlet about one mile wide. The 

 water of these lakes is fresh. 



If a canal be made, these lakes will be used as the 

 Bitter lakes are now used for the Suez canal. 



By a little dredgiug they will shorteu the canal, about 

 thirty miles, and form a large, safe, and commodious harbor. 



The sand bar, which separates them from the sea, is in 

 some places, only five miles wide, and may be easily 

 crossed by a small additional length of canal, if the speed 

 of the current at that natural outlet called Boca del Barro, 

 of five miles an hour, should be thought an impediment to 

 the entrance, and exit of ships. 



The entire country from the mountains to the Pacific is 

 of alluvial soil, except those portions nearest the sea, which 

 are of sand. There is no rock anywhere on the surface. 



The climate is hotter and drier than on the Atlantic slope, 

 and not so favorable toward any kind of vegetable growth, 

 or miasma. The greatest pests are the . sand flies, called 

 rotadores, half as large as musketoes, but twice as trou- 



Trans. vii.~] 21 



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