16 
ENGINEERING REPORTS. 
portion of the Isthmus. The Jaltepec and Jumuapa rivers are 
separated by a chain of highlands, constituting a spur from the 
Cordillera on the west, and extending easterly to the Coatza- 
coalcos ; branching from this main ridge, are numerous lateral 
spurs, which, decreasing in width and height, gradually srbside 
to the level of the river-bottoms. We also find the country bor- 
dering the Sarabia River considerably elevated and broken, 
from its confluence with the Coatzacoalcos to a point about two 
miles westward of Boca del Monte ; and three miles S. W. of 
this latter place is a high range of hills, known as the mountain 
of Sarabia. 
Further to the south are the hills of Xochiapa, which origi- 
nally seem to have formed a connected chain, joining the moun- 
tain range to the east and west, but have been cut through or 
divided by the Malatengo, Almoloya, and Chichihua rivers; 
thus opening natural passages through a range of hills, which 
otherwise would seem to have offered an almost insuperable 
obstacle to the construction of a railroad. Between this range 
and the .Summit Pass, the country is made up of elevated roll- 
ing plains, which are divided by low ranges of hills into three 
divisions, known respectively as the plains of Xochiapa, Chi- 
vela, and Tarifa, which generally present a very smooth sur- 
face, but more or less undulating, and nearly destitute of 
heavy timber, except on the margins of the principal streams. 
They gradually become more elevated as we approach the Sum- 
mit Pass, and also present a more uniform level surface. 
They are bounded on the south by the cerros Prieto, Masahuita, 
and Espinosa, all of which terminate in rugged limestone peaks, 
at an elevation of from 1500 to 2000 feet above the Pacific ; anc 
form the only connecting links between the high mountain chain 
extending westwardly through the State of Oaxaca, and the 
Cordillera of Guatimala on the east. 
By a narrow opening or gap in these mountains, we descend 
suddenly from the elevated table-lands to the Pacific plains, 
which form the third or southern division. These plains aver- 
age about twenty miles in breadth, from the base of the mount- 
ains to the Pacific coast, and descend on the meridians to the 
lagoons, at an inclintion varying from ten to fifteen feet in 
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