76 Bulletin of Laboratories of Denison University [Voi. xi 
cent quartzite. This series, which must at one time have been 
continuous with the same formation in the Magdalena region to 
the west, the Limitar region to the north and the Sandia, Man- 
zana region to the north-east, is here exposed only as a mere 
fragment in the side of the mountain-escarpment, where its up- 
turned edge is exposed as it dips into the mountain, that is, to 
the west. Small as is the extent, the exposure is a good one 
and has afforded a large number of fossils. Near the bottom is 
the horizon of Productus cora and Spirifer opimus. The section 
at this place is as follows : 
The limestone is capped by flows of brecciated material that 
speak of explosive volcanic activity. These flows are of trach- 
ytic nature but are not the first of the volcanic outbursts to 
which the mountain owes its origin. The trachyte rears its head 
to the height of 8000 feet in the form of a high promontory 
from which a sharp ridge extends westward for over a mile, 
forming the northern wall of an ancient crater of great extent. 
The flows from the crater have extended to the northward in 
descending cascades and gentle streams to the point where the 
range is abruptly cleft by the Nogal canon. To the north still 
was another trachyte volcano which has left a mighty spur 
known far and wide as strawberry Peak. This volcano also had 
its period of tremendous explosive outbreak as is shown by the 
great mass of breccia and talus-conglomerate collected in the 
region to the northeast and laid open by a second canon to the 
north of Nogal canon. 
Even in the amphitheatre of what we take to be the seat 
of the old trachyte volcano are here and there similar deposits, 
especially towards the north-east and south-east sides. These 
breccias and talus conglomerates yield on erosion most fantastic 
and architectural forms and the castellated peaks and odd mural 
shapes are characteristic of the deposits. Plate X, from the 
south side of the great crater-like area refered to and on the 
south side of the Blue Canon road, gives an idea of the condi- 
tions. As already said, the trachyte period was not the earliest 
stage of eruptive activity. The proof of this assertion is found 
in certain obscure but important masses of andestite found usu- 
