1 1 8 The American Geologist. AugU8t * 1905 
it is not believed that any of thtm are of clastic origin. 
Some of them are certainly aplitic ; and others are known to 
be quartz-veins inclined at low angles. 
According to the writer just mentioned, the rocks im- 
mediately north of the boundary line in Colorado are pre- 
dominantly hornblendic schists, though there are some mica 
schists present. These schists occupy the middle and high- 
est portions of the axis. On the east side of the range 
gneisses and gneissoid granites prevail, together with some 
mica schists. A coarse-grained granite is also frequently 
met with. 
Southward, within the limits of New Mexico, the horn- 
blendic schists become less and less prominent. At the 
boundary line the Azoic belt is not more than 6 or 7 miles 
in width, but within a short distance it rapidly broadens out 
to 20 miles. The prevailing rocks are dark and light colored 
gneisses, some bands of the latter very closely resembling 
beds of quartzite. Occasionally bodies of coarse-grained 
granites are met with. 
Bordering the front of the Rockies, from a point near 
the northern boundary of New Mexico and extending south- 
ward a distance of over 30 miles, is a rugged ridge known 
as the Cimarron range. These mountains are composed 
largely of Tertiary eruptives. Where the range is deeply 
cut by canyons which traverse it, as for example on the 
Rayado, the Cimarron, and several branches of the Vermejo, 
Azoic rocks are disclosed beneath the spread-out eruptives. 
These old crystallines are chiefly light colored micaceous 
schists and dark hued fine-grained gneisses. Occasionally 
these rocks are broken through by coarse-grained red 
granites. « 
Tn-tbe southern part of the range the base of crystal- 
lines is covered by basalt flows from the great Ocate crater, 
which rises out of the plains a few miles to the southeast- 
ward. 
The areal distribution and the structural relationships 
of the Azoic basement in the southern part of the Cimarron 
range are at present somewhat obscure. The apparent irre- 
gularities in the distribution of these rocks is probably due 
largely to the presence of the Mora arch which extends in a 
