458 



SCIENCE. 



[N. S. Vol. XIV. No. 351. 



it is certainly desirable that discussions of the 

 Basin range structure should include a consid- 

 eration of the criteria for the demonstration of 

 faults by this means, when only one member of 

 the faulted series is visible. Yet no such con- 

 sideration of the problem is given by Spurr. 

 He confirms earlier work by finding that mar- 

 ginal faults are not to be determined along the 

 base of the ranges (except in rare instances) by 

 ordinary stratigraphic evidence. He reiterates 

 the undisputed fact that great erosion has oc- 

 curred since the ancient folding and faulting 

 within the body of the ranges, and he illogic- 

 ally infers from this that recent faulting, mar- 

 ginal to the ranges, has not taken place. In- 

 stead of dealing with the problem at issue — the 

 sufficiency of physiographic evidence to prove 

 block faulting— he asserts without adequate 

 discussion the sufficiency of erosion to produce 



upon it to attest its elevation. The block fault- 

 ing of the Basin ranges may perhaps be some 

 day disproved, but not until the evidence of 

 faulting accepted by Gilbert and Russell has 

 been shown to be valueless. 



PHYSIOGRAPHIC EVIDENCE OF FAULTING. 



The essential elements in the physiographic 

 evidence of faulting in the Great basin are the 

 impossibility of accounting for the presence of 

 the mountain ranges if the interment depres- 

 sions have been produced by erosion alone, and 

 the ease of accounting for them if the rough 

 form of the region has been blocked out by 

 faulting, leaving erosive processes only the 

 smaller work of trimming the mountains into 

 their present shape. The difficulty of dispens- 

 ing with faulting is both qualitative and quan- 

 titative. In the first place," the structure of the 



Fig. 1. Diagram of a mountain carved on a faulted block of previously deformed and denuded strata. 



existing forms, and after the briefest consider- 

 ation he denies the peculiar faulting that has 

 been reasonably inferred on physiographic 

 grounds to be essential for the production of 

 the ranges. This is very much as if one should 

 deny the modern uplift of the Appalachian 

 Piedmont district after its broad denudation, 

 because no strata containing marine fossils lie 



ranges is commonly oblique to their border, so 

 that the faulted margin passes indifferently from 

 one structure to another, as in the accompany- 

 ing figure ; if the ranges were the residuals of 

 a long period of undisturbed erosion, such a 

 lack of correlation between border and struc- 

 ture would not be looked for ; but if the ranges 

 are limited by faults at one side or both, the 



