1 12 Bulletin of Laboratories of Denison University [Voi. xi. 
to be basic, it is intersected with acid dykes that may be de- 
rived from the same source as the granite of the northern peaks. 
These acid dykes in a basic rock carry a small quantity of gold 
as is the almost universal rule under these circumstances. Ex- 
tensive superficial prospecting has resulted in opening no impor- 
tant mines thus far. To the east the Cretaceous sandstones and 
shales occupy the surface for many miles and, in one locality a 
few miles east of Cerrillos, there is a considerable area covered 
with the silicified trunks of large trees — in short a buried and 
petified forest is exposed. The trunks are frequently only par- 
tially exhumed by erosion and protrude from the sandy matrix 
in a horizontal position. The Omera coal banks fourteen miles 
to the east and south of the railroad have at various times been 
extensively worked but at present the coal shipped by the Santa 
Fe comes entirely from the extensive mines at Madrid two or 
three miles south of Cerrillos. The detailed study of this in- 
teresting region is reserved for a special paper. The rocks are 
of Cretaceous age and consist of about 150 to 200 feet of alter- 
nating shales and sandstone. The higher layers are often of a 
yellow freestone not unlike the Waverly rock of Ohio in ap- 
pearance. 
The whole is much disturbed and faulted and seems to 
have been covered by a flow of basic material of varying thick- 
ness which in some place has given place to a crag of materials 
derived from the erosion of this sheet. Immediately above the 
anthracite is a thin bed of a black basalt-like intrusive that 
seems to have qeen injected between the strata or to have cov- 
ered the roofing .shales of the coal. It may be that this sheet is 
to be connected with the dyke above mentioned. It is a ques- 
tion whether the superficial sheet of phonolite (?) has had much 
part in the metamorphism of the coal though that seems to be 
the local theory. Passing to the south, the gray igneous rock 
assumes greater importance and occupies all the foot hills to the 
granitic or gneissic core of the Ortiz range. The Cretaceous 
bounds the mountain on the northwest and the entire western 
base is apparently occupied by the Carboniferous. 
A deep valley separates the Ortiz from the San Pedro 
