38 The American Geologist. jan.isgo. 
tance apart of the fossils is only three-fourths of an inch. 
All of the cylindrical casts in this exposure are flattened as 
stated; nor have I found in the thousands of fossils exam- 
ined in the matrix, in different exposures, a single exception. 
From these facts we must conclude that the cylindrical 
casts of Scolithus, in the original horizontal sand beds, were 
flattened by enormous pressure, exerted in a direction at right 
angles to the trend of the strata, prior to the uplifting of the 
formation. No other supposition is tenable, no matter what 
we infer the original shape of Scolithus cavities and casts to 
have been, whilst this partially explains the present density of 
the quartzite and at the same time fully accounts for the 
observed fact that the elongation is uniformly in the direction 
of the strike of the upturned strata. 
Of course other conclusive proof of the direction and extent 
of such pressure has long been given, but I do not think that 
any one, prior to this, has called attention to the striking 
testimony of Scolithus. At any rate, if any one else 
observed it, I have failed to find any account of such discovery. 
It may be well to state, in conclusion, that the writer's ob- 
servations have not extended any further than to the quartzite 
of York county, Pa. 
EXTINCT VOLCANOES IN COLORADO. 
By Arthur Lakes, Golden, Col. 
Although we have abundant signs of volcanic activity in 
past ages in Colorado on a grand scale, the general absence of 
true volcanic craters has been frequently noticed by those famil- 
iar with the geology of the state. Most of our igneous rocks 
belong to the class that have been erupted through fissures, 
from which in some cases lava has poured over the surface, 
the vents being filled by dykes. If craters ever existed on the 
surface line of these fissures, all traces of them have for the 
most part long ago been removed by erosion. The dyke at 
Valmont and the basaltic cap of the Table mountains at 
Golden and of the Raton mesas at Trinidad are examples. 
These surface eruptions are mostly confined to the more re- 
cent forms of lava, such as basalt and dolerite. Another and 
larger class embracing the older eruptions of porphyry and 
diorite, appear to have come up through fissures, but never to 
