AMERICAN GEOLOGY SURVEYS UNDER POWELL. 



621 



During- the years 1874, 1875, and 1876 Capt. Clarence E. Dutton, of 



the Ordnance Department, U. S. Army, made, under direction of the 



Powell survey, further studies in the plateau region which had already 



received attention from Powell, Newberry, and others, 



Dutton's Work on . ' • ' 



the High Plateaus, as previously noted. Dutton s monograph — a Report 

 on the Geology of the High Plateaus of Utah, a quarto 

 volume of 307 pages, with an atlas — appeared under date of 1880. 

 The particular territory studied b} T Dutton lay in Utah, occupying a 

 belt of country extending from a point about 15 miles east of Mount 

 Nebo, in the Wasatch, south-southwest for about 175 miles, and having 

 a breadth of from 25 to 80 miles — a total area of some 9,000 square 

 miles. 



As was the case with Powell, as indeed must here be the case with 

 every observing man, Dutton was impressed with the evident signs of 

 the vast amount of erosion which the country had undergone within 

 comparatively recent geological times. Not- 

 ing that from an area of 10,000 square miles 

 from 6,000 to 10,000 vertical feet of strata 

 have been removed, he fell to speculating on 

 the probable effect upon the earth's equilib- 

 rium of such a transference of materials. 

 If the slow accumulation of great masses of 

 sediment on sea bottoms brings about a 

 gradual subsidence, why should not, he 

 argued, the removal of a like load from any 

 land area result in a corresponding uplift 

 or elevation. Thus, for the second time in 

 the history of American geology, was 

 broached the now well-known subject of 

 isostacy. (Seep. 499.) This great erosion, 

 it is well to note, he regarded as having taken place mainly in Miocene 

 time, though continuing on into Pliocene. 



He noted that the great structural features of the high plateaus were 

 due to faults and monoclinal flexures; also that the one form of dis- 

 placement passed continually into the other — that what is here a simple 

 fault passed by subdivision, but a few miles farther along in its course, 

 into what he designated as step faults, and still farther on into unbroken 

 anticlinals. All of these grander displacements belonging to the same 

 sj'stem he regarded as having their commencement in the latter part 

 of Pliocene times. 



The great amount of volcanic activity evident received attention, 

 the most ancient dating back to Eocene times. The character of the 

 volcanic products was studied and the various lavas classified as (1) 

 propylite, (2) andesite, (3) trachyte, (1) rhyolite, and (5) basalt, 

 named here in order of their extrusion. The facts, as a whole, in this 



Fig. 118.— Clarence Edward Dutton. 



