238. GROVE KARL GILBERT— DAVIS [MBMOffiS r$£x^ 



the modification that his original views suffered in view of the suggestions later made by Powell 

 and Dutton. The brevity of his original discussion in the Wheeler report was regrettable, as 

 has been shown in an earlier section of this memoir; his silence during the following period when 

 others were debating the origin of the basin ranges is more regrettable still. His reticence is, 

 as already noted, probably to be explained in part by a dislike of controversy, and perhaps still 

 more by a feeling that, as he had had his say, he ought not to speak again on the subject until 

 he had new opportunity of field study. If this be true, it is all the more unfortunate that he 

 was not assigned in 1893 to field work in the Great Basin, for there, as well as in Colorado, a good 

 number of topographic sheets were awaiting a geological coloring. 



GILBERT AS CENSOR 



\ 



Gilbert's reaction upon the announcement of the dissenting opinion was to ask for an assign- 

 ment to field work in the Great Basin for the summer of 1901; his studies then made wdl be 

 summarized below. In the meantime it is interesting to read his own opinion on the subject 

 before his return to the field. Following its excellent custom, the Geological Society submitted 

 the dissenter's essay to several censors before accepting it for publication; and of these censors 

 Gdbert was one. One of his letter books fortunately preserves a copy of his typewritten report. 

 After an introductory statement to the effect that different views obtained regarding the origin 

 of the basin ranges, the report reads substantially as follows: 



The earlier view [Gilbert's own] is that the ranges were made by uplift, the crustal blocks which underlie 

 and compose them being lifted with reference to the blocks beneath the adjacent valleys, and usually divided 

 from them by profound faults. Mr. Spurr's view is that the mountains were made by the erosion of the bounding 

 valleys. After a careful reading of Mr. Spurr's paper and a review of the subject I find myself decidedly of the 

 opinion that his view is erroneous and that the earlier view, especially as modified and restated by King, Dutton, 

 and Russell, is in substantial accord with the main facts, including those adduced by Mr. Spurr in this paper. 

 The considerations on which this opinion is based will be set forth in the following paragraphs. 



1. Relation of Trend to Strike. — It has been satisfactorily shown that the Appalachian ranges are mountains 

 of erosion in the sense which Mr. Spurr uses that phrase and I take them as a type. They have been developed 

 by erosion from a broad mass of strata which had been previously folded, and also to some extent faulted. As a 

 result of differential erosion valleys have been produced along the outcrops of the less resistant rocks and mountain 

 ranges along the outcrop of more resistant rocks. The characters of the mountain ranges are a direct consequence 

 of their mode of origin: (1) Each range is crested from end to end by a single bed or by a compact series of beds; 

 (2) The trend of the range is identical with the strike of the composing rocks; (3) The range continues as far as 

 the formation continues. ... In respect to these characters the Basin ranges are contrasted with the Appa- 

 lachian ranges. The Basin ranges as a rule are less simple in internal structure. In many of them the crest line 

 shifts repeatedly from one formation to another. Anticlines and synclines often traverse a range obliquely, and 

 the associated ridges, whether anticlinal, synclinal or monoclinal, run to the margin of the range area and there 

 stop abruptly. In other words, fold and fault systems, more or less analogous to those of the Appalachian 

 province, are found within individual ranges of the Great Basin system; but the strike of such a structure 

 system is usually more or less oblique to the trend of the range, and the faults and folds are cut off abruptly at 

 the margin of the range. . . . 



In my judgment these characters take the Basin ranges out of the class typified by the Appalachian 

 ranges. . . . The trends of the Basin ranges are not dominated by the strikes of constitutent formations, and 

 it is probable that the valleys are not so dominated. It is quite conceivable that, in any individual case, the 

 original position of a river (superimposed or antecedent) , may have been oblique to the strike of the formations, 

 and that a great [intermont] valley may have been developed by the river and its tributaries. But in the broaden- 

 ing of such a valley the lateral branches would become adjusted to the strike [of the weaker beds], and the sides 

 of the [intermont] valley would be characterized in detail by strike ridges. If the floor of such a valley were 

 subsequently buried by detritus, the resulting detrital plain would be invaded on both sides by tapering strike 

 ridges. If the valleys of the Great Basin were formed in such a manner the line separating their detrital cloaks 

 from the rocks of the adjacent ranges would be serrate instead of simple. Each of the oblique monoclinal or 

 anticlinal ridges composing a range would project into the valley, and each of the mountain valleys would contain 

 a bay of detritus; there would be a gradual passage from rocky range to detrital plain, instead of the abrupt 

 transition along a simple line so characteristic of the region. In accounting for the oblique transection of folds 

 the erosion theory seems to me full of difficulties and the fault theory comparatively free from difficulty. 



2. Unpaired Monoclinal Ridges. — The portion of a Basin range adjoining a valley often consists of a mono- 

 clinal ridge with the escarpment toward the valley and the dip away from the valley. By Mr. Spurr these 

 ridges are interpreted as the halves of anticlinal arches and the complementary halves, not being visible, are 

 supposed to have been removed by erosion. ... I doubt if subaerial erosion has ever accomplished such a 



