Geological Reco?i?ioissa?ice in N. M. — Hcrrick. 339 
Our route after crossing the Albuquerque mesa and the 
valley of the Rio Puerco, was south-westward. Rising through 
the Cretaceous sandstone in the Rio Puerco valley some 
twelve miles south of San Ignatio is a curious volcanic peak of 
a red color and marked on the government map as "red sand- 
stone hill." This is the sole member of the trachyte series 
of eruption seen in the whole region. It is quite dififerent 
from the basalt cones elsewhere in evidence and is greatly al- 
tered. The metamorphic action on the penetrated strata is 
also very pronounced, while the effect of the basaltic intru- 
sives is usually comparatively slight. Incidentally this expos- 
ure afifords proof elsewhere difficult to obtain directly of the 
post-Cretaccous age of the trachyte eruptives. 
Continuing south-east toward the Arroyo Salado the route 
passes over the edges of the Cretaceous, the dip here being to 
the north-east till in the abrupt escarpments presented to the 
valley of the Rio San Jose and easily seen by the passenger on 
the Santa Fe and Pacific R. R., the red series is exposed 
throughout its entire thickness. At the base at the foot of 
Mesa Negra there are limestone and lime-breccia beds inter- 
calated between sands and shales of red and green. These un- 
doubtedly belong to the Permian and are merged above into 
hard red sandstone. Above this sandstone is a layer 25 feet 
thick of green and chocolate sandy shales followed by 75 to 
100 feet of fine pink sand, this by 25 feet of loose white sand, 
and this, in turn, by 20 feet of yellow ochraceous sand. Then 
follows the peculiar vermicular gypsiferous shales which in- 
variably precede the gypsum beds. Here the shales are about 
10 feet thick, while the gypsum is so eroded that it is difficult 
to estimate the thickness, but it is probably between 75 and 
100 feet. At this zone, as elsewhere, salt is evidently present, 
for the springs which issue from the sandstone below are high- 
ly impregnated with salt. The springs at the foot of Mesa 
Negra, for example, are surrounded by incrustations of quite 
pure salt and the water itself is very distinctly saline. The 
same thing is true of the springs along the entire escarpment. 
Above the gypsum appear the chocolate beds which bridge 
the interval between the top of Mesa Negra and Mesa Gi- 
gante in whose perpendicular face the upper or vermilion beds 
appear. We cannot at this time give accurate measurements 
