Review of Recent Geological Literature. 5 7 
The Cerrillos hills are laccoliths of hornblende-and augite- 
andesyte which have been intruded in Cretaceous sediments. The 
over-arching sediments have since been removed by erosion, leav- 
ing the igneous core exposed. Mr. Johnson is the first to suggest 
a. laccolitic origin for these hills which have been considered by 
earlier geologists to be remnants of great dykes or of old volcanoes 
in which the core has been partially eroded. He asserts as proof 
of his conclusion the following facts: 
1. The absence of eruptive fragments in the associated strata. 
2. The compact crystalline texture of the rock which is hard, 
dense and in places almost granitoid. 
3. The dip of the strata away from the hills showing tilting 
subsequent to deposition. 
4. Intrusive tongues of lava in the adjacent beds. 
5. Metamorphism in the beds resting on the laccoliths. 
6. The quaquaversal dip around the laccoliths. 
7. The relation of the intrusive sheets accompanying the lac- 
coliths which are thicker near the uplift and thinner and less 
steeply inclined at a distance from it. 
8. The evidence of annular drainage as shown in the San 
Marcos Arroyo. 
The Mesozoic sediments surrounding the laccoliths cover a suc- 
cession of deposits extending from the lowest beds, found at the 
base of the Galisteo monocline and presumably of Jura-Trias age 
through the Laramie deposits of Galisteo red sandstone. During 
the Fox Hills period there was a deposition of lignite which has 
been altei'ed subsequently to bituminous and anthracite coal by 
the metamorphic action of the intrusive sills. There followed a 
long erosion interval during which the andesyte was intruded and 
the region peneplained. The deposition of the Santa Fe marls be- 
gan and continued from the Loup Fork stage until recent times. 
These were supposed to have originated in one of the great lakes 
that were so numerous in the western interior during Tertiary times. 
The author however, suggests that these marls are of alluvial 
rather than of lacustrine origin and advances in support of this 
theory the following proofs: 
1. The variation in texture and composition of the beds in 
vertical section. 
2. The presence of beds of conglomerate. 
3. The sudden variations in thickness and extent of the com- 
ponent beds. 
4. The presence of erosion unconformities. 
5. The development of cross bedding. 
6. The presence of land fauna. 
7. The absence of a lake schoreline. 
To Mr. Johnson the above facts seem conclusive. While these 
