i 
1-926 Some Peculiarities of the Local Drift, etc. (November, 
slopes left in side-gulches by the retreat of the diminutive glaciers. 
Existing glaciers in the Wind River mountains and in the San 
_ Juan mountains (S. W. Colorado), enable us to witness the actual 
-~ production of some of these peculiar effects and to understand more 
clearly how defragation' has played a very important part in the 
rough chiseling of mountain features in the far West. 
The general southward trend of the glacier-cut cafions is very 
marked, although numerous side-gulches follow more or less 
“transverse courses. In Northern Wyoming, at the close of the 
Glacial Period, the old Tertiary lake basins were still in condition 
to receive and assort the material deposited by the melting ice, 
and the greater part of the drainage was easy, but in some 
cases in the interior of the mountain masses to the northward, 
narrow, elongated basins were ploughed out below the general 
. drainage, although very few of these now exist in which an out- 
let has not since been made. In the heart of the Wind River 
mountains a remarkable structuré of this kind is to be seen 
nearly opposite old Camp Brown, at the head of the North 
fork of the Popo-agie river, near the base of Fremont’s peak. 
Here two of these deep, narrow cafions run parallelwise for 
several miles, with small glaciers still acting upon their shaded 
sides, the drainage from one being to the Missouri tributaries, 
the other feeding affluents of the Colorado drainage. In South- 
A = ern Colorado somewhat similar features are apparent, but the 
ree ry much com- — 
The same 
~~ 
_ Juan features are not repeated exactly in any othe : 
as my observation goes. The distinctive peculiarity lies m 
-duplex character of the erosion; that is to say, there are jas 
zones of glaciation vertically, the upper largely representing 7 
rans portative action, the lower being eroded without re 
the débris to any great extent. The imperfect drainage had ee: 
tened the ice-sheet so that it could move asa unit only we 
perficial portion, while the lower part acted like a slowly wor*” 
down of masses of rock 3 
propose this term to express the breaking igen. ing or gti ; 
- of gorges, as distinguished from the ordinary abrading oF S 7. 
