22 
GEOLOGY 
of the Rocky Mountains. After going through the Pass, which is fifteen miles long, we come out 
in the plain of the Rio Grande del Norte, where the Granite is found covered with Drift vtni Allu- 
vium, which form the whole plain as far as the right hank of the river, where the formation is 
Sandstone. This Sandstone is white, friable, horizontal in stratification, and forms almost the whole 
of the bottom of the valley which lies between the Rocky Mountains , the Sierra de \ emez and 
Mount Taylor or Sierra de San Mateo. On some points, as at Galisteo, it is covered by a grayish 
schistose clay, containing nodules of iron and numerous plaquettes, composed of fragments of Jno- 
ceramus shells and fragments of scales and bones of fishes, belonging to the genus Ptychodus. In this 
Sandstone and Clay, which rest horizontally on the upheaved beds of the Trias, the Jurassic and the 
Carboniferous , are found the remains of Ammonites Novi-Mexicani ; Scaphites ; Inoceramus Lerouxi; Os- 
trea congesta', Tellina occidentalis Mort.; Cytherea Missouriana Mort., and the teeth of a superb Pty— 
chodus Whipplei, which indicates, for the relative age of this formation, the Cretaceous Kocks, and 
further , the group of the White Chalk of Europe. 
This fact is a new one in the Geology of America, where, until now, the true Chalk has not 
been recognized ; and now the Cretaceous Hocks are found to be composed of four divisions , pre- 
cisely as in Europe: the Meocomian, which I have found on the Canadian , the False Washita, hort 
Washita and near Preston, Texas; the Green-Sand of Timber creek, near Philadelphia; \\\e Marly- 
Chalk of Rordentown, New Jersey, of the Bad Lands (Mauvaises Terres), Nebraska, and of Fort 
Washita; and finally the White Chalk or Craie Blanche of New Mexico. 
Besides, the discordance of stratification of the Upper Cretaceous of New Mexico, with ail 
the sedimentary rocks found there, indicates that this formation was deposited after the principal 
dislocation of the Rocky Mountains, which took place at the end of the American Jurassic period. 
From the Rio Puerco to the Sierra Madre, our route was constantly upon beds of Trias and 
.furassic, which are often covered in this region by immense overflowings of lava, coming from 
the ancient extinct volcano of Mount Taylor*), that is seen some distance to the North. These 
streams of lava which spread over the bottom of the valleys are exactly similar to the streams 
from volcanoes in actual activity, and, like these, are destitute of vegetation, and give to the 
1) The first extinct volcano that I met with in exploring the Rocky Mountains is I'oumi between Ga- 
listeo and Pena Blanca. It is named Cerrito and is situated in the middle of the Rio del Norte valley, 
as a connecting link between the Sierras of Santa Fe, Yemez, Sandia and Placeres. This ancient vol- 
cano is not verv elevated, the different cones of which it is composed being only 800 or 1000 I'eet above 
the plateau from which they rise; the lava extends over the whole country between the rivers Galisteo , 
Cieneguilla, Naule and the Pueblos of Cochiti and of San Felipe: the ranchos of Cerrito are even at 
the bottom of the crater. The Rio del Norte and the Rio Bajado or of Cieneguilla have made their beds 
in the lava of the volcano , and in the sections discovered by these means, it is seen that the streams 
of basaltic lava have recovered the Drift and in some places even have changed it into volcanic con- 
glomerate. 
Between the Rio Grande and the Rio Puerco, a little north of Albuquerque , there is a volcanic cone 
whose lava extends over the Sandstone which is the equivalent of the White Chalk , and whose streams are 
seen as far as the old Pueblo of San Felipe , on the top of the hill opposite the town of Albu(]uerque , 
and on the right side of the road from Albuquerque to the Rio Puerco. 
There are several volcanic cones where the route to the Pueblo of Zuni crosses the Siena Madre , 
and 30 miles further south a large volcanic cone is seen with two or three secondary ones near it. 
* ■ 
