TOURTELOTTE PARK SPECIAL MAP. 103 
that the striz were formed during the progress of this movement. The 
question, then, which naturally arises is, Is the fault progressing faster in 
its upward movement than are the processes of erosion in their degrading 
action, or has erosion simply acted more vigorously along the fault plane? 
If the latter is true, it must be that the erosion which has produced this 
“escarpment is post-Glacial, for any glacial action would inevitably have 
abraded the polished surface and removed all traces of the strie. Judging 
from the effects of post-Glacial erosion as exhibited elsewhere in the district, 
and even in the vicinity of the butte, one must conclude that it has not 
been nearly so great in amount as to be able to accomplish such a work; 
and even if such an amount of work were possible the same objection 
holds good as in the case of glacial erosion, namely, that during the other 
processes of degradation the striz along the fault plane must have been 
obliterated. 
The talus at the foot of the cliff was examined to see what might be 
its main source, and it was found to consist almost entirely of fragments 
derived from the Parting Quartzite or from the overlying Carboniferous 
rocks. The distinction in lithological character between the dolomite of 
the Silurian and that of the Carboniferous is usually slight, but in Castle 
Butte there seems to be a distinction in texture by which the two rocks 
may be separately recognized; and judging from this, there appears to be 
in the talus very little material derived from the Silurian. 
On both sides of the fault at this point are rocks which have about the 
same degree of resistance to erosion, for opposite the Silurian dolomite in 
the cliff there lies the corresponding dolomite of the Carboniferous. There 
is therefore no apparent reason why erosion should have attacked the rocks 
to the south of the fault more vigorously than to the north. Moreover, the 
peculiar freshness of the strize at the bottom of the cliff and the progressive 
effacing of these marks toward the top, together with the fact that the 
amount of erosion becomes progressively greater and greater to the very 
top of the butte, is evidence that the erosive forces have acted longest at 
the top of the escarpment and practically not at all for a distance of 75 or 
100 feet from the bottom; and even at the top the amount of erosion has 
been comparatively slight. The only explanation of this seems to be that 
the scarp actually represents the entire amount of throw of the Castle Butte 
fault, and that this fault has come about almost entirely since Glacial time. 
