78 
BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
_Interfluye Surface 
Terrace Slope 
UP | 
hel | | | 
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i ond 
& 
Fig. 6. Terrace slopes on the south side of Rapid Creek where it emerges from the Bighorn Mts. 
of the gravels in question; 
ducted a reconnoissance in northwest 
Wyoming a few years ago and later 
papers have been published by F. E. 
Matthes, R. D. Salisbury and E. Black- 
welder, and N. H. Darton (b and d). 
Other scattering references were found, 
which are not available at the time of the 
present writing. Scant account is given 
for these 
papers are devoted chiefly to the discus- 
sion of other problems. Where the 
gravels are mentioned, they are referred 
to the Quaternary period. 
Stores. The interfluve' surfaces of 
the gravel deposits appear to be closely 
related to the somewhat gentler slopes of 
the upper portions of the front rampart, 
as though, in a previous period of erosion, 
the mountains had been reduced to & 
lower relief than that of the present and 
the cloaking gravels had been spread 
along their flanks at a faint angle. Now 
both mountain slopes and gravels have 
been deeply incised and shoulders, more 
or less well defined, on the sides of the 
gateways by which the streams emerge 
from the mountains, mark the level at 
which the later cutting began. Succes- 
sive stages in the down-cutting are reg- 
istered in the terraces cut in the gravels 
and the underlying rock. The down- 
valley slopes of the terrace plains are 
steeper than those of the interfluve sur- 
faces. On the south side of Rapid Creek 
(Plate 4), a comparison of the interfluve 
slope with that of a well-marked terrace 
plain below showed the angle of the 
former to be five degrees while that of 
the latter is ten degrees (Figure 6). 
1A term used by Professor Davis to indicate the 
uncut portion of a slope between two consequent 
streams. 
