academy of scimch] WHEELER SURVEY 59 



What may have been the original altitude of the ranges we have no means of knowing, but there is evidence, 

 along the margin of the system, that their elevation was not all accomplished at once, and it is not impossible 

 that progressive elevation and denudation, as they have opposed, have also measurably counterbalanced each 

 other (63). 



No specific statement of the measure of upheaval is given, apparently for the good reason 

 later noted that " all estimates of the magnitude of mountain movements are so involved with 

 considerations of erosion, that it would avail little, even were the material at hand, to attempt a 

 full presentation of individual examples" (126). Reference to the evidence for progressive 

 upheaval above noted as provided by certain marginal ranges will be alluded to in a later 

 section. 



UPHEAVALS AND ERUPTIONS. 



Reference has already been made in the account of the Zufli dome to the somewhat 

 reactionary nature of Gilbert's views regarding the origin of mountains by upheaval through 

 the operation of deep-seated, vertical forces, instead of by compression through that more of 

 superficial, horizontal forces. These views evidently apply even more fully in the case of the 

 basin ranges, as the foregoing paragraphs have shown. Some additional passages may now 

 be introduced to show that the deep-seated forces, of which the upheaved domes and fault 

 blocks were taken to be the surf ace effects, were believed to have been closely associated, in the 

 western part of the basin range province at least, with the deep-seated forces that produced the 

 extensive volcanic eruptions of that region. After several pages descriptive of the lava over- 

 flow in Nevada, which "over large areas have buried all other rock masses," the following 

 generalizations are presented: 



A most important feature of these eruptions is their association with the ridges [ranges] of corrugation. 

 The great majority of vents are along lines of upheaval. . . . The law that the distribution of lavas is in sym- 

 pathy with the ridge [range] structure, rests on too broad a basis of facts to be vitiated by its exceptions. More 

 than this, there seems reason to believe that uplift and extrusion are, in a certain degree, mutually complemen- 

 tary, or equivalent. The highest ranges, as a rule, are (comparatively) non-volcanic, and those ranges, or 

 portions of ranges, which exhibit the greatest eruptions are endowed with but low nuclei of other material. 

 Where, in tracing a range, we find its crest exchanging non-volcanic rocks for volcanic, we do not find the latter 

 heaped upon an undiminished ridge of the former, but rather replacing it, as it gradually or suddenly diminishes 

 in height; and the case is strengthened by the consideration that, while the low, buried portion of the nucleus has 

 been guarded by its mantle against the forces of. denudation, the higher part has been exposed to a continuous 

 waste. ... It does not necessarily follow from the coincidence, in place, of uplift and eruption, that the sub- 

 terranean loci of the action which has produced corrugation are identical with the volcanic sources. If, however, 

 it be shown that along lines of disturbance there is an inverse quantitative relation between uplift and outflow, 

 a strong argument is adduced, not merely for the identity in location, but for the absolute identity of the up- 

 heaving and volcanic forces; for, if the two modes of mountain building are complementary actions, they must 

 be regarded as co-ordinate manifestations of the same agency. 



These passages close with an illustration of the admirable candor which later became more 

 and more a characteristic of Gilbert's style of presentation: 



It is by no means easy to demonstrate this interrelation of upheaval and eruption. My own confidence 

 that it exists is derived from the comprehensive review of my notes, referring to about fifty of the Basin Ranges, 

 and is a result of inspection rather than analysis. I know not how to present the material to the reader — without 

 special pleading — so that it shall have the same force (125-126). 



EROSION OF- THE UPHEAVED RANGES 



An incautious phrase, quoted with its context near the end of the second preceding section 

 to the effect that "the upper strata, by continually adapting themselves, under gravity, to 

 the inequalities of the lower, have assumed the forms we see," might be mistaken to imply 

 that the upheaved basin-range blocks still retained their surfaces and scarps of upheaval little 

 changed, were it not that the work done by post-faulting erosion is elsewhere especially con- 

 sidered. That such erosion was understood to be of prime importance in fashioning the exist- 

 ing ranges is plainly shown by a later quotation in the same section. This essential factor 

 had, furthermore, been already briefly touched upon in connection with an earlier statement 

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