or 
ie) 
‘Chihuahua. It is 
a * 
380 New Merico and California. 
fifty miles south of El Paso the limestone seemed to cease, and 
: rocks of the most varied — and combinations continued 
ere as far as Chihuahua, interrupted sometimes only by granitic 
The base of the porphyry is i feldspar. 
Chihuahua and some distance to the south ead west of it, in 
7A 
the Sierra Madre, porphyritie rocks predominate, and valuable mines 
nd in them 
are fou 
Near Chihuahua, as I understéod, about twelve miles northeast of it, 
mountains of limestone appear ; nd through the favor of Mr. Potts, 
in. Chihuahua, I received a piece of limestone from there, containing 
some casts of the chambers of an Orthoceras, feo. that this limes 
stone belongs also to the Silurian system. Mines are also fons in it. 
Another fossil I received i in cg said to come from 
e near elt mining place about 250 miles neon at 
D quinquicostatus, (Sowerby,) of the cretace- 
ous series ; but not jenihe travelled eg ugh that part of the state, I om 
not able to give any comment upon i 
Saucer Chihuahua to Matamoras, sails with the army as a sur- 
geon, my time was so occupied that I could not make any’distant excur- 
sions from the road ; debe! the geology of the country seemed to 
be very uniform and uninteresting. : 
¥ ihuahua some distance south, porphyritic rocks continued. 
In Saucillo, (70 miles from Chibuahua,) : aessired the first lime- 
stone again.” From there to Santa Rosa passed some hills of 
amy pdaloidal basalt, but the main chain - the mountains was all 
limestone, and éowtinoed to be so throughout the whole eastern rami- 
fication-of the Sierra Madre, over which we travelled from here down 
to Saltillo and rit Se where the low country begins. ‘This lime- 
stone forms steep, often rugged mountains, rising on an average 2,000 
feet above the plain; it is metalliferous, and has all the Ap poanall of 
the Silurian limestone, found at El Paso and Chihuahua, but I was 
never able to discover any fossils on this route. . Silver and lead 
mines are of various occurrence in it; in the limestone surrounding 
Cadena, coal has been found, as I was informed, but 1 had no time to 
verify it 
From. Monterey to the seashor I made one interesting discovery 
near Mier. Qn the bank of the Alamo rie about four od above 
its mouth into the Rio G rande, I found an extensive bed of large 
fossil shells of Ostrea, belonging to the cretaceous formation. As the 
me formation has lately * ‘found by Dr, Remer, of Berlin, to 
extend in og from the San Antonio to the Brazos, this cretace- 
dus bed ne scl Pica in all probability a continuation of is In looking 
over the rece 
Grande below Laredo, tes “entire hills are to be seen, compose 
almost wholly of what appears to be a collection of large sea oyster 
shells.” I presume, therefore, that the same cretaceous formation eX- 
tends in this direction higher up on the Rio Grande.—pp. 135-138. 
_In farther illustration of’ the ounty we cite. some i 
graphs from other om of the e Report. 
