LARAMIE REGION, WYOMING 
difficult to prove that the plane surface is 
the result of planation rather than of 
structure. 
That the Sherman peneplain in the 
typical locality is of later age than the 
mid-Tertiary formations is indicated by 
the fact that it passes directly across 
the embayments of Tertiary sediments 
along the east side of the arch. If the 
tops of the plateaus farther east are a 
part of the same plain, as seems probable, 
we have additional evidence in the fact 
that there also the Tertiary beds are 
truncated by this surface. ‘There is, 
therefore, basis for the opinion that the 
age of this peneplain is late Tertiary, or 
more exactly that it has been made since 
the middle of the Miocene epoch. What 
connection the Sherman peneplain may 
have with the Eocene surface is very 
difficult to determine. It is probable 
that the Sherman plain truncates the 
older surface over the Sherman arch, 
while eastward the relation is reversed, 
and the Sherman plain lies high above 
the buried Eocene surface. 
Passing to the east side of the Medi- 
cine Bow plateau, we again meet some 
features suggestive of the topography of 
the Laramie uplift. On the slopes of 
Jelm Mountain flat spurs are cut upon 
highly inclined schists at a level nearly 
1,000 feet below the plateau surface. 
These seem to correspond roughly with 
the flat top of Red Mountain and, 
farther east, with the plateau surface of 
Boulder Ridge. If the Sherman pene- 
Ww 
& 
4Y1GH PLAINS. 
LARAMIE ARCH 
LARAMIE BASIN 
MEDICINE BOW PLATEAU 
TSS 
Ww 
Fic. 5.—Section showing supposed relation of the Tertiary erosion surfaces to the present topography, in the latitude of Laramie. 
(a, Medicine Bow surface; b, Sherman surface; c, Leslie valleys.) 
7 
