Art. V .5 Herrick, Geology of New Mexico, 1 1 1 
intrusives. Here, for example, at the base of the exposure are 
6o feet of dark, horizontal, Cretaceous shales intersected by 
nearly vertical narrow dykes of what looks like a basalt though 
much decomposed. The strike of such a dyke about two feet 
wide near the road to Santa Fe is N. lo degrees W. Above 
these shales is a bed of crag and loose material over 50 feet 
thick. The bowlders at the bottom of this series are of phono- 
lite similar to that of the mountains at the south end of the 
range. The whole is capped by 25 feet of recent lava from the 
adjacent cone. The basalt dyke referred to stops short at the 
top of the shales showing the upper loose zone to be of later 
date than the intrusive. The shales, which dip to the east at a 
distance from the mountain, become horizontal as they near the 
range and, near its base, dip to the west. We may assume that 
the phonolite uplift, at least the later part of it, occurred after 
the deposition of the Cretaceous and that the later deposits 
(perhaps Pleistocene) result from the erosion of the resulting 
materials. The extensive dykes radiating from the mountains 
and cutting through the strata may therefore be of the same 
age as the main mountain uplift. Though the northern and 
higher peaks of the range are of granite it is probable that this 
uplift is parasitic upon the basic eruption. 
At Waldo, about three miles west of Cerrillos, at a point 
about a third of a mile north of the track, is a prominent moun- 
tain of porphyritic gray eruptive which shoulders its way through 
the dark Cretaceous shales. From this region a strong dyke 
extends southward and is apparently the same that intersects 
the coal workings of the Cerrillos Coal Co., near the breaker, 
and may be the principal cause of the special metamorphism 
which has transformed the bitumenous coal to anthracite at this 
place. This dyke is about twenty feet wide and is a prominent 
landmark. The other hills of the Cerrillos range between 
Waldo and the town of Cerrillos seem to be, for the most part, 
composed of the same basic eruptive as is the country to the 
northward nearly to the foot of the granite mountains of the 
northern part of the group. The country for two miles or more 
north of the town is broken and, while the country rocks seem 
