NATIONAL ACADEMY BIOGRAPHICAL MEMOIRS VOL. VIII 



formity; it therefore represents the logical and necessary 

 growth of the science. ... It seems especially unwise for 

 the exploring geologist to commit himself in early stages of 

 investigation to refined and exact correlations, and in practice 

 it is found that a great number of local names are used tenta- 

 tively until further research demonstrates approximate identity 

 or establishes diversity." 



fRpwell was one of the pioneers in the demonstration of the 

 almost undisturbed continuity of deposition in the West from 

 Cambrian to Tertiary time, sometimes slightly interrupted by 

 gentle unconformities, but without trace of the "revolution" 

 that, from the structures known in Europe and eastern North 

 America, had been previously supposed to mark a world-wide 

 break between the depositional records of Paleozoic and Meso- 

 zoic times^/ He was the first to bring out the great structural 

 features of the Plateau province, already referred to. He re- 

 peatedly emphasized the action of uplifting rather than of 

 compressing forces, for he had chiefly to do with broad struc- 

 tures of nearly horizontal strata, limited by faults or, as he so 

 justly remarks, their homologues, monoclinal flexures; and 

 the latter style of deformation was in his time a geological 

 novelty. Complicated deformation was mostly limited in the 

 Plateau region to "zones of diverse displacement" between ex- 

 tended areas of little disturbance; the only sharp folds with 

 , which he had to do occurred in these narrow zones. He sug- 

 gested that flexing of strata was probably a deep-seated process, 

 while faulting was a more superficial one. As in his discussion 

 of the problem of antecedence, stated above, so through all his 

 writings, he strongly supported the then growing idea that 

 "upheaval was not marked by a great convulsion, for the lifting 

 of the rocks [in the Uintas] was so slow that the rains removed 

 the sandstones almost as fast as they came up." 



Following his systematic habit of mind, he grouped the 

 mountainous reliefs of his region into two great classes ; some 

 were composed of sedimentary strata and others of extrav- 

 asated materials. He then divided these classes into a num- 

 ber of types according to details of structure, and subdivided 

 them still further according to the work of erosion upon them. 

 The Appalachians were the only mountains here mentioned 



