GLACIATION IN THE BIGHORN MOUNTAINS 223 



stones and bowlders were found the surfaces of which had the 

 appearance of having been glaciated, but none which could be 

 regarded as decisive. The failure of distinct striae is perhaps 

 not to be wondered at, since most of the material is so deeply 

 weathered that but few of the bowlders retain much of the 

 original surface. Many of the bowlders, indeed, are decayed to 

 their centers, and many more have thick coatings of oxidized 

 material. Furthermore, in the younger glacial drift of the 

 present valleys, these same sorts of rock are striated but rarely. 



The drift-like material on Bald mountain is separated from 

 the Paleozoic terranes to the west by a valley 500 feet or more 

 in depth. Farther west, a valley 1,000 feet or more in depth 

 separates the Paleozoic terranes from the crystalline rock, whence 

 the debris in question was derived. Whatever its origin, the 

 drift appears to have reached its present position before these 

 valleys were excavated. Its topographic position therefore, as 

 well as its physical condition, points to its great age, an age 

 which must antedate the older body of certain glacial drift 

 {^Pg, Fig. i) by an interval of time greater than that which 

 separates the two formations of known glacial drift. 



Deposits which have some similarity to that on Bald moun- 

 tain have some development elsewhere, but nowhere else was the 

 suggestion of glacial drift so strong as on Bald mountain. 



RoLLiN D. Salisbury, 



Eliot Blackwelder. 

 University of Chicago. 



