academy or sconces] BASIN RANGES 241 



The mistakes in his own earlier work here referred to in third-person phrase probably lay 

 first, in the failure then to recognize the long period of erosion between the early epoch of folding 

 and the later epoch of block faulting, for in the season of 1901 he found abundant evidence of 

 such an erosional period, as will appear in quotations from field notebooks introduced below; 

 and, second, in the earlier assumption that block faulting had been accomplished chiefly by 

 vertical upheaval, an assumption which it was impossible to maintain in view of the moderate 

 inclination of the mountain-margin fault planes, as represented by spur-end facets in the 

 Wasatch and other ranges. It was probably an experience of this summer that was recalled 

 15 years later when Gilbert wrote to his elder son, who was then engaged in engineering work 

 in the dry country: 



The only remedy I know for a Utah desert wind is to camp in the lee of an irrigated farm, and that raises 

 the question of preference — mosquitos or dust. 



After stopping field work he made a visit to the Colorado Canyon with the director of the 

 survey, and went as far as San Francisco before returning to Washington. 



LOSS OF THE FIELD MAPS 



Work on his Alaska report appears to have occupied much time during the following winter, 

 but in December Gilbert spoke on " Western Utah " before the Geological Society in Washington, 

 when it is to be presumed he gave some account of his summer's work ; and at the end of the year 

 when the Geological Society of America met in his home city of Rochester, he presented a brief 

 paper on "Joint veins," illustrated by a much fractured rock from the House Range; this was an 

 example of the small-topic problems which he repeatedly discussed at scientific meetings in his 

 later life. It was in the following spring that, by a most unhappy accident, all the topographic 

 records of the work in Utah were destroyed, and this so'?seriously discomfited him that he stopped 

 further work on the basin ranges, published practically nothing on the campaign of 1901, and, 

 after completing his report on "Glaciers and glaciation" for the Harriman expedition, turned 

 from his old Great Basin problem to a newer one in California. Not until a year after his talk 

 on " Western Utah" did he make a more formal statement of the results he had gained in 1901 at 

 the Washington meeting of the Geological Society of America, in December-January, 1902-3; 

 he then emphasized the significance of the simple base line that characterizes the margin of cer- 

 tain basin ranges, regardless of their structure, and showed that such a base line proves the pres- 

 ence of a strong fault; at the same time he stated his belief that this feature had not been suffi- 

 ciently understood by others. Those who were present at this meeting will remember, and others 

 who were not there should be told, that Gilbert's manner when making his statement was the 

 gentlest possible, without a trace of controversial enmity. The printed record of the statement 

 in the Proceedings of the society is unfortunately nothing more than a perfunctory abstract which 

 occupies only nine hnes, and of these but four bear closely on the problem at issue: 



Evidence of block faulting was shown to exist in extensive shear zones, in triangular facets truncating the 

 ridges in front, and in the even linear bases of the ranges. That the faulting is still going on is shown by displace- 

 ments in the recent alluvium. 



Not a word about the long period of erosion between the early folding and the later faulting; 

 not a word about the replacement of upheaval with little compression by upheaval with great 

 horizontal extension. But both these important modifications of his early views are clearly 

 indicated, one in his notes, the other in a later, much later, reference to the origin of the basin 

 ranges, as will be shown in later sections, where a change in the statement as to linear range 

 bases will also be found. 



Gilbert did not again take up the basin-range problem until the last four years of his life. 

 It was as if the loss of the topographic records had for the time completely thwarted him in the 

 attempt to return to and extend his early studies in the western field. The disappointment 

 must have recalled to his own mind the regrets that he had felt 20 years earlier when Powell 

 summoned him from Utah and placed him in charge of Appalachian geology. But he was un- 

 complainingly silent in the matter; even his nearest associates on the survey heard no word of 



