368 
Tlie American Geologist. 
Juiie, 190(1 
both lines of nonconformity may be seen on the same hill. 
Figure 6 represents an ideal section along a bluff north of 
the Platte river, opposite Louisville. On one side of the ra- 
vine the line between the Carboniferous and the Dakota is 
near the base of the bluff, at H, while on the other side the 
same line is at least fifty feet higher at the point K. 
Not infrequently a third nonconformity may be observed. 
The later deposits on the tops of the bluffs have been washed 
down forming alluvium, and have partly filled up the chan- 
nels of the recently cut ra\'ines, as indicated along the line 
Fig. 7. Recent Alluvial Deposits. 
E. F. Fig. 7. In this case the nonconformity is between the 
alluvium above and the older rock below, be it Carbonifer- 
ous, Dakota or Glacial. 
These nonconformities are the more interesting because of 
their geographical location. In the region of the plains, 
where most of the strata lie comparatively level, exposures 
of rock of such widely different ages in the same localit)' 
are quite rare. The only other place in the region where 
two marked nonconformities may be seen in connection, so 
far as I have been able to observe, is in the Comanche Cre- 
taceous areas in southwest Kansas, where the Permian Red- 
beds, the Comanche, and the Tertiary are exposed. Even 
there, however, such patent examples as are found on the 
Platte may be sought in vain. 
The University of Nebraska. April 20th, i goo. 
