46 
ENGINEEEING EEPOETS. 
very direct, and the maximum grade sixty feet per mile : for 
two or three miles of this distance the line encounters a succes- 
sion of deep ravines and intervening spurs, involving rather 
heavy cutting. 
To the south, the descent is much more gradual, and the 
character of the work similar to that between the Sarabia and 
Jumuapa rivers. 
The excavations on that portion of the line extending from 
tfye Jumuapa to the Jaltepec river will be mostly in a gravelly 
clay soil, that can be easily worked ; there will, however, be 
considerable rock excavation at the crossing of the main divid- 
ing ridge. The formation at this point is a compact, earthy 
limestone, overlying a coarse conglomerate or pudding-stone : 
this latter is mainly composed of rounded flint, and hornstone 
pebbles and boulders united with a calcareous cement. The 
limestone formation is most abundant near the intersection of 
the Amate and Suchil picaduras, where it extends two or three 
miles in a north and south direction. The stone has a porous 
structure, but is quite hard, and is found in compact beds of 
considerable thickness, the plane of stratification being nearly 
horizontal. In connection with this rock we find extensive beds 
of fossil madrepore. 
On the northern slope of the highlands, separating the Ju- 
muapa and Jaltepec rivers, the pudding-stone constitutes near- 
ly the entire rock-formation ; this is everywhere covered with 
a rich mould, sustaining a luxuriant growth of vegetation. 
The country lying between the rivers mentioned, presents many 
interesting features. The streams, in some instances, have tun- 
nelled through hills of solid limestone, and at other points have 
worn out extensive caverns in this rock, ornamented with beau- 
tiful stalactites, and which furnish secure retreats for the wild 
beasts abounding here. 
This rock also frequently forms sharp, rugged peaks, rising 
to a height of two or three hundred feet above the level of the 
intervening valleys. The summits of the long, narrow ridges 
which constitute the most striking feature in the topography of 
this part of the country, are often very sharp, sometimes having 
a width of only three or four feet at top, and descending ab- 
