DHE GROLOGY OF GE WEE SANDS Ora Niy 
MEXICO 
East of the San Andreas and Organ mountains of New Mex- 
ico is an extensive valley that has been the subject of much dis- 
cussion from the practical as well as the theoretical point of 
view. The writer is not aware that any competent geologist 
has had the opportunity to make an exhaustive study of its 
unique features and ventures to put on record the results of a 
somewhat careful if cursory examination of the valley and its 
environs. 
Our first visit was made by wagon from Socorro, the seat of 
the county of the same name, by a route which afforded ample 
opportunity to observe the varied geological conditions of the 
region to the north and east. East of the Rio Grande, after 
leaving the immediate valley of the river, the Tertiary red marls 
are encountered, and lie in rather low terraces upon the foot of 
the greatly disturbed red beds of Permian and Triassic age. 
These beds are tilted and greatly faulted, leaving one in doubt 
as to the sequence at this point, especially as there are curious 
beds of fire clay and shale filled with a varied flora of carbonif- 
erous habit consisting of numerous species of Lepidodendrids 
as yet not worked out specifically. 
The lower part of the Permian is composed of limestones 
and sandstones capped by anhydride and gypsum beds, the for- 
mer being in some places massive and upwards of fifty feet 
thick. Extensive exposures of what is apparently carbonifer- 
ous limestone constitute the principal axis of the low range at 
this point, and are followed by the red beds over a large area on 
the eastern side. These beds, as everywhere in the territory, 
are impregnated with salt and saline alkalis as well as gypsum. 
The springs are nearly always salty, and lower flats are covered 
with “alkali.” Passing southward, in the immediate valley of 
the Rio Grande, near San Antonio, is the remarkable basin of 
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