GEOLOGY AND MINERALOGY. 
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into hills a few hundred feet high, and having a dip southwest 
of about 20°. These are repeated at the Indian village of 
Almagres, where the strata project into the river a little below 
the town. The limestone is here light, porous, and decomposed 
by the weather. 
About fifteen miles north of the sandstone conglomerate, and 
west of the Coatzacoalcos, a fine-grained sandstone, whitish and 
very light, appears over ground. It is porous, and' too soft to 
be used for any architectural purposes, but may possibly serve 
in the arts as a polishing material. This rock, on which Tesis- 
tepec is placed, covers an area of eight or ten miles square. 
The sloping plains have here an elevation of 200 feet above the 
Gulf : in their descent they suffer little deviation, as the land is 
but little elevated into hills on the western side of the river. 
At the Penas Blancas and the Cerrito de Cuapinoloya, the 
white sandstone strata are almost horizontal. 
The Sierras, in which the Coatzacoalcos and its eastern trib- 
utaries take their rise, were not accurately explored. Atra- 
vesado, which is 5016 feet high, has its summit of porphyry : 
the hills more northward reach 7680 feet, and are sienitic. 
Clay and talcose slates form the larger portion of the whole, 
while the flanks and lesser hills are made up of sandstone, 
porphyry, quartz, and greenstone. The compact limestone skirts 
the whole range. Micaceous granite occupies a few hills, and 
serpentine is met with in some places. Besides these, amyg- 
daloid rocks, hornstone, obsidian, jasper, and petroleum, are 
met with in the bed of the rivers which have their sources in 
these hills. 
Augitic rocks form no unimportant portion of these hills. 
The basaltic sand which is washed down by the streams, occa- 
sionally contains gold particles. Such was the case with that 
from the hacienda of San Jose, in a brook emptying into the 
Tanchochapa. Near San Jose are tjie remains of sinkings for 
wells, which, it is believed, have been used by the natives in 
former times for washing these auriferous sands. It is well 
known that the basaltic sand at Trinity Bluff, California, is very 
rich in gold ; but it has been separated with great difficulty by 
washing, owing to the density of the sand. Skilful chemical 
