236 GROVE KARL GILBERT— DAVIS [MEMOIES [Vo A L T xxt 



scarps piedmont to a number of basin ranges was mentioned by Russell in his monograph 

 on Lake Lahontan, and was of course well known to Gilbert. A brief account of these small 

 "fault cliffs" is given in Gilbert's essay on the " Topographic features of lake shores," where 

 it is shown that they differ from level-based shore cliffs in that they do not follow "exact con- 

 tours but ascend and descend the slopes of the foot hills." They are described in some detail in 

 the Congress excursion guidebook, and it has already been told that they were made the subject 

 of special examination when the excursion party reached Salt Lake City. 



More important than the discovery of the small and recent faults in the piedmont alluvium 

 was the recognition of a new kind of topographic evidence for faulting that is provided by the 

 facets which truncate the extremity of many spurs along the western base of the Wasatch Range; 

 for these facets were taken to represent little altered parts of the great fault plane on which the 

 mountain mass has been upheaved. The date of their recognition is not recorded; they were 

 first announced in 1890 in the Bonneville monograph, as follows: 



The western front of the Wasatch is determined by a great fault. From the line of this fault . . . springs 

 a steep face of solid rock, the escarpment of the up-thrown orogenic block. At intervals the rock face is divided 

 by narrow clefts or gateways, whence streams issue from the interior of the range. Between each pair of adjacent 

 streams is an acute ridge of rock, whose roof-like cross-profile marks it as the product of aqueous sculpture. 

 The end of each is truncated by the great fault, and the truncated terminals, standing in line, constitute the 

 rock face at the margin of the [piedmont] plain (307). 



The recognition of the existence of these terminal facets was an important step in the 

 study of the visible landscape; the explanation of their origin was an important step in the 

 rational physiography of the lands. When once noticed, they are conspicuous enough, inasmuch 

 as some of them rise several hundred feet over the mountain base; and better still, when they 

 are once understood they become positively attractive features of the mountain view, because 

 the eye turns with so much pleasure to those elements of a landscape which the mind understands. 



Yet significant as are the well-preserved terminal facets of the Wasatch spurs, no mention 

 was made of the occurrence of similar forms on the spur ends of any of the basin ranges, either 

 as initial, lit tie-worn facets, or as rounded and dissected facets; and no general statement was 

 published concerning the share taken by spur-end facets in the theoretical aspect of the basin- 

 range problem. They were introduced only as a side issue in a problem of an altogether different 

 nature, and after their brief introduction little more was said of them. Even in the chapters on 

 the Great Basin region which Gilbert prepared for the Congress excursion of 1891, no mention is 

 made of the facets, but the large facets of some strongly truncated spurs were pointed out to the 

 excursionists as their train, on its way southward and eastward after leaving Salt Lake City, 

 approached the Wasatch front to enter the Canyon of Spanish Fork on the way through the range. 



A DISSENTING OPINION 



Such was the incomplete status of the basin-range problem, as far as Gilbert's own pub- 

 lished contributions to it are concerned, when the whole subject was brought to the foreground 

 of his attention by the work of a member of the survey who had had wide experience in the West 

 and who presented an essay at the meeting of the Geological Society of America at Albany at 

 the end of December, 1900, traversing the earlier explanation of the ranges by faulting. 3 The 

 dissenting opinion thus announced seems to have arisen largely from the adoption of a geological 

 rather than a physiographic method of approach to and treatment of the questions at issue. 

 In common with certain members of the Fortieth Parallel survey, the dissenter from Gilbert's 

 views believed that "many of the Great Basin ranges were probably formed ... at the close 

 of the Jurassic . . . contemporaneously with the Sierra Nevada" (248); he thus not only 

 ascribed great antiquity to existing mountain masses, but failed to distinguish with sufficient 

 clearness between the ancient date when the deformed structures within the existing mountain 

 masses were produced and the modern date when the existing mountains were developed as 

 topographic forms. He knew of the composite theory which, following King, dates the folding 

 of the mountain strata as Jurassic, and which, following Gilbert, dates the upheaval of the 



1 J. E. Spurr. Origin and structure of the basin ranges. Bull. Geol. Soc. Amer., xii, 1901, 217-270. 



