a 138 
tains of limestone appear; and through the favor of Mr. Potts, in Chi- 
nae aoc a piece of limestone from there, containing some casts 
- of the chambers of an Orthoceras, proving that this limestone belongs also 
to the Sitarias system. Mines are als o foun 
Another fossil I received in Chihuahua, ia: i come from the limestone 
near Corralitas, a mining place about 250 miles northwest of Chihuahua. 
It is a Pecten quinquecostatus (Sowerby,) of the cretaceous series ; but 
not having travelled through that part of the State, 4 am not able to give 
any comment u 
From Chihuahua to Matamoros, travelling with the army as a surgeon, 
my time was so occupied that 1 could not make any distant excursions _ 
from the road ; but sporseritad — the geology of the country seemed to 
be very uniform and uninteres 
P ihuahua some apes south, the porphyritic rocks continued. 
In Saucillo (70 miles from Chihuahua a) I perceived the first limestone 
ao 
tinued to be so througheut the whole eastern ramification of the Sierra 
Madre, over which we travelled from here down to Saltillo and Monterey, 
where the low country begins. ‘This limestone forms steep, often rugged 
mountains, rising on an average 2,000 feet above the plain ; it is metallif- 
erous, and has all the appearance of the Silurian limestone, found at el 
Paso and Chihuahua, but I was never able to discover any fossils on oom 
route. Silver and lead mines are of various occurrence in it; in the lim 
Stone surrounding rete coal has been found, I was informed, but 1 
had no time to veri 
From Monterey to shes seashore | made but one interesting discovery ; 
near Mier. On the bank of the Alamo river, about four miles above its 
mouth into the Rio Grande, I found an extensive bed of large fossil shells 
of Ostrea, belonging to the TRE formation. As the same formation 
has late ely been discovered by Dr. Roehmer, of Berlin, as extending in 
cate om the San Antonio to the ae this cretaceous bed’ near Mier 
7h. 
“entire hills are to be seen, ¢ composed almost wholly of what appears to 
be a collection of large sea oyster-shells.” I presume, therefore, that the 
same + Spacey se formation extends in this direction higher up on the Rio 
