The Fundamental Complex -Keyes. 1 1 5 
position and geological age of the basal crystallines in many 
of the different mountain ranges there are some instances in 
which there exists but small doubt as to their Azoic posi- 
tion. The general proofs are in a measure comparative. 
They are the relative amount of metamorphism evidenced, 
the character of the deformation apparent, the difference in 
petrographical features, the geological relationships, the ab- 
sence of all evidences of clastic origin, and a comparison 
with similar features of known areas in other parts of the 
country. 
The literature relating to New Mexican Azoic forma- 
tions refers all the basal crystallines to the Archaean. Lit- 
tle of definite value therefore can be gleaned grom the wide- 
ly scattered published descriptions of local phenomena. The 
first suggestion that any portion of the ancient crystallines 
occurring within the boundaries of New Mexico were any 
other than of Archaean age is believed to be a recent state- 
ment regarding the significance of the recent identification 
of certain "quartz-reefs" in the Sandia mountains as highly 
metamorphosed sandstones.* 
The present surface exposure of the great crystalline 
basement underlying all the fossilferous strata in New Mex- 
ico is relatively small. Aside from the area in the south- 
ern Rocky mountains in the northern part of New Mexico 
the exposures of pre-Cambrian rocks are confined almost to 
linear outcrops found along the immense fault-scarps of the 
block mountains. Some of these outcropping faces indicate 
that the rocks are of undoubted Azoic or Archaean age, 
while others are manifestly of clastic nature and thus belong 
to the Proterozoic. 
In order to understand more fully this apparent anoma- 
lous distribution it is necessary to refer to some of the gen- 
eral conditions prevailing in neighboring states that the 
geological history discloses. The conception is that the 
upper surface of the ancient crystalline basement in this 
region represents an old peneplane on which, when submer- 1 
gence took place in Proterozoic times, an enormous thick- 
ness of sedimentaries was laid down. This whole country, 
still in pre-Cambrian times, was folded up into mountain 
Eng. and Mining Jour. vol. lxxvi, p. 967, 1903. 
