62 GROVE KARL GILBERT— DAVIS [MEM0IE \ vo A ™xt 



singular conclusion was emphasized by the statement that corrugation, which was produced 

 in the Appalachians chiefly by folding, was produced in the basin ranges chiefly by faulting. 

 No hint was given of an earlier period of folding separated by a long erosion interval from a 

 later period of faulting. The recognition of a long interval, but without mention of its erosional 

 work, was made in 1878 by King, who, after referring to his previous description of the basin 

 ranges as a "series of folds," and then crediting Powell and Gilbert — priority of naming being 

 here given to the senior geologist rather than to the junior as author of the fault-block theory — 

 with having "called attention to the abundant evidence of local vertical faults and the resultant 

 dislocation into blocks," added: "Yet when we come to examine with greater detail the structure 

 of the individual mountain ranges, it is seen that this vertical dislocation took place after the 

 whole area was compressed into a great region of anticlinals with intermediate synclinals. In 

 other words, it was a region of enormous and complicated folds, riven in later time by a vast 

 series of vertical displacements, which have partly cleft the anticlinals down through their 

 geological axes, and partly cut the old folds diagonally or perpendicularly to their axes." 2 King 

 must have known that more or less erosion would have taken place between the times of folding 

 and faulting, but he did not mention it specifically, probably because he, like many of the older 

 geologists, was more interested in subsurface structure than in surface form. 



VIEWS OF POWELL AND DUTTON 



It was, then, the custom of the time that no special attention should be given to the erosion 

 that must have taken place between the folding and the faulting, or to the forms produced by it. 

 Yet the recognition of that essential phase of the problem had been previously announced by 

 Powell, who briefly but clearly stated that, although the ranges of the Great Basin consist 

 largely of Eozoic and Paleozoic rocks, their form and height show that they are of very late 

 upheaval, the Great Basin before their upheaval having been "a comparatively low plain, 

 constituting a general base level of erosion to which that region had been denuded in Mesozoic 

 and early Tertiary time when it was an area of dry land." 3 A somewhat more explicit state- 

 ment to the same effect was made by Dutton a few years later: 



The flexures of the Basin Range strata are not, so far as can be discovered, associated with the building of 

 the existing mountains in such a manner as to justify the inference that the flexing and the rearing of the ranges 

 are correlatively associated. On the contrary, the flexures are in the main older than the mountains, and the 

 mountains were blocked out by faults from a platform [the rocks of] which had been plicated long before, and 

 after the inequalities due to such pre-existing flexures had been nearly obliterated by erosion. 4 



The recognition thus given to a period of erosion between an earlier epoch of mountain 

 making by folding and a later epoch of mountain making by faulting marks the beginning of a 

 modern conception of mountains that has found wide application in later years; so wide, 

 indeed, that it is now difficult to find any mountain range which exhibits forms due to folding 

 and erosion alone, without a later period of upheaval and more erosion. Fundamental as this 

 conception of two epochs of deformation separated by a long period of erosion is in the explana- 

 tion of the basin ranges, it is manifestly not due to Gilbert. He, however, cites the extensions 

 of his original theory proposed by King and Dutton — but not the extension proposed by Powell — 

 in his posthumous essay and adds : 



The idea that the Great Basin district, corrugated by folding at the close of the Jurassic, had been reduced 

 by erosion to a condition of low relief, aids the conception that the mountains of today were created by the 

 later and disruptive deformation. It is distinctly Dutton's addition, although King had paved the way for it. 



Then, after noting the confirmatory evidence found by Russell in the young fault-block 

 ranges of southern Oregon, he goes on: 



It is a remarkable fact that during the development of a theory as to the essential structure of the ranges, 

 the observers [including himself] who reported on the existence of faults gave no adequate statement of the 

 evidence on which their determinations were based. 



> Geological Survey of the Fortieth Parallel, I, 1878, 735. 



> Geology of the . . . Uinta Mountains, 1876, 32. 



* Geology of the High Plateaus of Utah, 1880, 47; also 7. 



