The Fundamental Complex — Keyes. 121 
character of the crystalline basement are presumably simi- 
lar to those of the Organ mountains, immediately to the 
south, which have in fact a genetic relationship to the San 
Andreas range. 
While properly a continuation of the San Andreas and 
the Franklin mountains to the south the Organs belong to a 
distinct block which has been elevated much more than any 
other portion of the long ridge to which they belong. In 
consequence the sedimentary rocks have been entirely re- 
moved except at the very base on the west side. 
The rocks of the Organ mountains are chiefly red and 
gray, coarse-grained granites. Associated with these are 
hornblendic and micaceous schists, which are traversed by 
numerous dikes, which are quartzose, dioritic and andesitic 
in character. Proterozoic quartzites and clay slates are 
well developed a few miles to the south, in Texas, and it 
is probable that these also extend into New Mexico. Ac- 
cording to Walcott the thickness of the pre-Cambrian 
clastic section is over 3,000 feet. 
In Perry's notes* on the geology of the Mexican 
boundary mention is made of the granites underlying the 
Carboniferous limestone of Franklin mountain north of El 
Paso and in the Organ mountains, but no specific refer- 
ence is made to their age. G. B. Shumardt passed through 
the Organ mountains in 1857 and noted on the east side 
hornblende and mica schists, and red and gray granites, 
all of which were cut by dikes of quartz, greenstone and 
porphyry. 
Thirty miles west of the San Andreas range the Ca- 
ballos mountains rise abruptly above the Rio Grande valley. 
These form a block mountain in which the crystalline base- 
ment is exposed for a vertical distance of 1,500 feet. Riotitic 
schists, gray crumpled gneisses, and granites form the 
principal rocks. The granites are of two principal kinds. 
One, which is more closely identified with the gneisses, is 
gray, rather fine-grained and contains a large amount of 
quartz. The other is a coarse-grained, red granite, which 
appears to be a late intrusive, though it does not penetrate 
• United States & Mexican Bound. Sur., vol. i, pi. ii. p. 8. 1857. 
t Jour. Geol. Obs. Texas and New Mexico, in 1855-6. p. 113, Austin. 
1886. 
