LENADO SPECIAL MAP. 121 
of the folding and the formation of the Silver fault, and that the movement 
of that fault resulted in cutting off the blue limestone and a portion of the 
dolomite. 
The first of these suppositions appears impossible, for the thickness of 
the blue limestone on Aspen Mountain and in Tourtelotte Park is from 100 
to 150 feet, and this formation is known to extend a long distance to the 
south of this point. North from Aspen Mountain, however, the blue lime- 
stone disappears in the bottom of the valley between Aspen and Smuggler 
mountains, and is not found at any point north of the Roaring Fork in the 
area examined. It is not probable that a formation having the considerable 
thickness above referred to should naturally die out in such a short lateral 
distance. The second supposition has more evidence in its favor, for there 
is known to have been an important upheaval and erosion interval between 
the deposition of the Leadville limestone and that of the Weber shales. 
During this interval the beds must have been in many places eroded, 
and it is not unlikely that in certain places whole formations were stripped 
away. It may be that in this way the Leadville blue limestone was 
removed over the Lenado area, and that the succeeding deposition of 
the Weber shale took place immediately upon the dolomite. The third 
supposition has fully as strong evidence in its favor, however, as has the 
second, for the contact of shale and dolomite is invariably, not only in the 
Lenado area, but throughout the whole district, a fault contact, and its char- 
acter shows that the movement along it has been very great, the amount of 
brecciation being greater than would result from a slight movement. Ina 
fault of so great magnitude it would be very easy for the plane of greatest 
movement to deviate locally from the plane of the bedding, and this devia- 
tion would produce the differences in the rocks on both sides of the fault 
which have been observed. A very slight deviation of this kind might, by 
faulting, remove whole formations. 
It may be possible that both the latter Ae are in a measure 
true, and that some of the lack of uniformity results from an unconformity 
below the Weber and some of it from faulting. The facts, however, are 
sufficient for most purposes, namely, that in the contact between the Weber 
and the underlying rocks there has been invariably, so far as observed 
in this district, a fault of great actual displacement which, on account of its 
parallelism to the bedding, or close approach thereto, does not exhibit any 
