ACADEMY OP SCUKCEB] WHEELER SURVEY 65 



As to the geological phases of his work, no warrant can be found for an interlineation to 

 the effect that he recognized, even though he did not announce, two periods of Great Basin 

 deformation and their separation by a long interval of erosion. His views on that side of the 

 subject were definitely enough expressed, and they were, as he himself clearly acknowledged, 

 defective. It is for this reason declared, at the opening of the present review of the basin- 

 range problem, that the more novel truths he contributed to it were physiographic and not 

 geologic. Yet, curiously enough, a clue to the overlooked elements of the theory was pre- 

 sented near the eastern margin of the basin-range province in the Pahvan Range, which accord- 

 ing to his first report should, "perhaps, be considered a southern continuation of the Oquirrh" 

 Range, and which appears to be the example previously referred to without name, as affording 

 evidence that the elevation of the ranges "was not all accomplished at once" (63). This 

 range was described and figured as including in its western part a large underbody of deformed 

 and deeply denuded Paleozoic rocks, the moderately uneven eastward slope of which is covered 

 unconformably by Tertiary strata, dipping gently eastward; and from these occurrences the 

 points made by King and by Powell and Dutton might have been inferred ; but no such infer- 

 ences were made. 



Gilbert's theory of the basin ranges in its original form must therefore be regarded as 

 seriously incomplete; so incomplete, indeed, that one may feel surprise at the importance it 

 attained. But quite as remarkable as the incompleteness of the theory was the failure of his 

 contemporaries to recognize its incompleteness. The strong objections that were urged 

 against it by other observers were not advanced because certain essential elements were omitted, 

 but because certain elements that it announced were believed to be wrong; and the theory 

 that these objectors adopted was as incomplete as Gilbert's was. The fact is that both the 

 theories of the basin ranges then current represented geological science as it was developed at 

 that time; both were largely concerned with structure and little concerned with erosion. To- 

 day erosion enters as an essential element in the explanation of the basin ranges, and no theory 

 of their origin can be regarded as complete which does not give to this external process as full a 

 measure of the attention due to it as is given to the internal deforming process. But this 

 comment, so easily made half a century after the theory was propounded, could not have been 

 made at the time of propounding the theory. Viewed in the light of its own epoch, the theory 

 was an important step in geological progress, because it took account of the upheaval of indi- 

 vidual mountain ranges without compression at a time when mountain ranges were believed 

 to be the result of lateral compression. 



Gilbert's return to the basin-range problem in 1901 is described in a later section. 



