ASPEN DISTRICT MAP. 149 
munication with the bottom end of the shaft, and in others, where mining has been 
going on steadily, the two disjointed ends are connected by a short incline. Where 
the Della 8. fault passes up through the Park Regent there is one drift along the 
line of this fault. The square sets with which this drift is timbered assume the 
form of rhomboids so rapidly that the superintendent, in order to avoid trouble with 
the track, laid the rails on short ties instead of spiking them to the square-set sills, 
so that the track could be kept up level without any reference to the timber sets 
inelosing the drift. J inelose a little sketch [fig. 6] showing the timbers as they 
were originally placed and the position of the timbers after they have been in posi- 
tion from one to two years. 
DOLLA DELETION ELL A aM IN LY GGLL090 YGSOOVPILAIELEOOPATU GCA OL A OTM YLT ITIL 
Seen ep ey POLLS 2; Let pespgsgEsd VLOCGIGDLIEGLOC ATID ALTGELD TT CILIGE 
GLEE ELE: 
\ 
N 
NS 
\S 
MQ 
SWQAVY 
W 
\ \ RAN 
NAY 
SAAN 
UK 
SSMAVAWY 
AWS SN 
QQ 
LIRQNAAYY 
\ 
\: 
\ 
SS 
AWN 
\ 
WY 
\ W \ 
Fig. 6.—Deformation of drift in Della S. mine by movement along fault. 
In the Butte fault in Tourtelotte Park there seems to have been a 
movement in post-Glacial time of at least 400 feet. If, then, we can arrive 
at any approximation of the period which has elapsed since the disappear- 
ance of the ice sheet, we may have some measure of the recent rate of fault- 
ing. Warren Upham,’ after correlating the various estimates as to the 
period which has elapsed since the disappearance of the continental ice 
sheet from the northern half of North America, comes to the conclusion that 
it may safely be estimated at between six thousand and ten thousand years. 
Glaciation in the Rocky Mountains has been considered somewhat more 
recent, but the country around Aspen bears evidence of profound glacial 
activity in no very recent times. The whole of the district mapped has 
been glaciated, and the ice sheet must have been of enormous thickness, 
since it filled up the Roaring Fork Valley and overrode Smuggler, Aspen, 
1 Pop. Sci. Monthly, Dec., 1893, p. 161. 
