330 The American Geologist. J"'^'^- ^^os. 
ogy of Montana (1872, p. 85). In this same report Powell 
first made use of the expressions antecedent and consequent 
with reference to valleys, meaning, in the first instance, that 
the drainage was established prior or antecedent to^ the cor- 
rugation of the beds by faulting and folds, and in the sec- 
ond case, that the valleys had directions which were de- 
pendent upon the corrugations. Valleys which were formed 
by streams, the present courses of which were determined 
by conditions not found in the rocks through which the chan- 
nels are now carved, and which were in existence when the 
district last appeared above the sea-level, he called super- 
imposed valleys. He also here used for the first time the 
term base level of erosion, which he defined as "an imagin- 
ary surface inclining slightly in all its parts toward the end of 
the principal streams draining the area through which the 
level is supposed to extend, or having the inclination of its 
parts varied in direction as determined by tributary streams." 
He pointed out, also, that the region of the Grand Canon 
was, after all, the region of less rather than greater erosion ; 
that, had the country been favored with a rainfall equal to 
that of the Appalachian country, the entire area hight have 
been reduced to a base level which would be the level of the 
sea, though the evidences of such erosion might be almost 
wholly obliterated. 
In 1 87 1, 1872, with the aid of a Government appropria- 
tion of twelve thousand dollars, the organization known as 
the Survey of the Rocky Mountains was established, in 
rivalry with those of Hayden and Wheeler. At the head of 
this Powell remained until the three were abolished in 1879 
and the U. S. Geological Survey created, with Clarence King 
at its head. It was while carrying on this survey that G. 
K. Gilbert was detailed to study the Henry mountains in 
Utah, the results of which were brought out in the now clas- 
sic monograph relating to the Laccolithic Mountains. 
Powell's first observations on the geology of the Uintah 
mountains were made in 1869. In 1871, 1874, and 1875 he 
again personally visited the plateau region, the last time be- 
ing accompanied by Dr. C. A. White, The results of these 
later years of exploration are given in the quarto monograph 
On the Geology of the Eastern Portion- of the Uintah Moun- 
