ENGINEERING REPORTS. 
13 
The Isthmus of Tehuantepec is that portion of the Mexican 
territory which lies between the Gulf of Mexico and the Pa- 
cific Ocean, where the two seas approach the nearest to each 
other ; and comprises the eastern portions of the states of Yera 
Cruz and Oaxaca. 
From the mouth of the Coatzacoalcos, which discharges itself 
into the Gulf in 18° 8' 20" north latitude, and 94° 32' 50" lon- 
gitude west (from Greenwich) , to the harbor of Yentosa on the 
Pacific, situated in 16° 11' 45" north latitude and 95° 15' 40" 
west longitude, the distance in a direct line is 143^ miles. The 
coast-lines on either side have a general direction nearly east 
and west. 
In considering the Isthmus with reference to its general topo- 
graphical features, it may properly be said to comprise three 
main divisions, more or less distinct in their general character- 
istics ; the first, embracing that portion extending from the 
Gulf to the base of the Cordillera, and which may be called 
the Atlantic plains ; the second, comprising the more elevated 
or moimtainous districts in the central parts, and the third, 
including the level country bordering the ocean on the south, 
and known as the Pacific plains. 
The first division comprises a belt of country of some forty 
or fifty miles in breadth, lying contiguous to the Gulf-coast, and 
made up of extensive alluvial basins of exceeding richness and 
fertility, through which the drainage of the northern slope of 
the Cordillera discharges itself into the Gulf. 
The principal of these hydrographic basins is that of the 
Coatzacoalcos, which occupies the central portion of this divi- 
sion, and has a general direction of IS". 1ST. E by S. S. W. It is 
separated from the basin of the Tonala and Tancochapa rivers 
on the east, and the San Juan on the west, by a moderately 
elevated plateau or table-land, furrowed by numerous small 
streams, and generally covered with dense forests. These table- 
lands, with few exceptions, are not elevated more than two or 
three hundred feet above the sea-level. 
Conspicuous to the west of the Coatzacoalcos are the peaks of 
San Martin and Pelon, mountains of considerable magnitude, 
and constituting the most striking topographical features of this 
