ACADEMY OF SCIENCES] POWELL'S SURVEY 73 



as the great Water-pocket flexure in the lower land east of the plateau base, were examined in 

 some detail; and as these features are among the finest of their kind in the known world, the 

 season must have been of great profit; but no report was made upon it. That appears to have 

 been reserved by Powell for Dutton, who spent the summers of 1875, 1876, and 1877 in the 

 high plateau region, and whose excellent account of it was published in 1880. Gilbert's pub- 

 lished results concern only the Henry Mountains, which, lying east of the high plateaus, were 

 briefly examined in 1875, and more closely the following year, as will be told on a later page. 



During both these summers the change from the irksome restrictions under which Gilbert 

 had been working on the Wheeler survey to the favoring conditions afforded on the Powell 

 survey was greatly enjoyed. Under Wheeler, Gilbert's movements had been largely subordi- 

 nated to those of an expedition, the chief object of which was topographical mapping; he had 

 been hampered, not to say harassed, in his field work by military regulations, one of which is 

 illustrated by the incident of the lost carbine in the Colorado Canyon in 1871, already told. 

 Under Powell, he was given the freest possible opportunity to move, with a small party of 

 which he was the head, over whatever route he selected; and his own geological studies were 

 the main object in view. He could thus himself turn the pages of the great book he was reading, 

 and ponder on each page as long as he wished. Evidently his transfer from a survey conducted 

 by an Army officer under military regulations to a survey conducted by a civilian scientist 

 under very free conditions was as salutary as the Army officer had predicted and as the civilian 

 scientist had hoped. 



It is, however, not clear why Dutton and Gilbert were sent by Powell in the summer of 

 1875 to examine the same field, thus introducing into a single survey the duplication of work 

 that was complained of when committed by rival surveys. It may be that Gilbert, having 

 already spent a good part of the summer of 1872 in the high plateaus, recognized their blocked 

 structure to be in a measure intermediate between the broadly extended masses of essentially 

 horizontal structure in the Colorado Plateau — the plateau trenched by the Colorado River in 

 northern Arizona — -and the linear masses of deformed structures in the basin ranges; and that 

 he wished to see the plateau blocks again in the hope that they would throw fight on the basin- 

 range problem. In any case his visit of 1875 taught him much about the region, although a 

 good share of his time was spent on the denuded area east of the lava-capped highlands. It 

 is to be regretted that his results remain unpublished; but instead of writing a report on what 

 he had learned in the summer, he spent at least a part of the following winter in working up 

 illustrations for the Uinta Mountain report by Powell, who noted in its preface: "To Mr. 

 Gilbert, I am indebted for great assistance in the preparation of the graphic representation 

 employed." In the atlas accompanying this report, Gilbert is credited with Plate IV, a bird's- 

 eye view or block diagram of a part of the Uinta uplift, showing the actual topography of the 

 district in the foreground, and a stereogram of the imagined uplift, unworn, in the background; 

 and this is believed to be one of the earliest published examples of a compound block diagram 

 of such design. It is, therefore, one of the many novelties which geology and physiography 

 owe to the ingenuity and good sense of this self-trained investigator. 



While Gilbert's notebooks, five in number, of the summer of 1875 on the high plateaus, 

 show that he enjoyed much greater freedom in making records than had been possible under 

 Wheeler, generalized descriptions are nevertheless rare. The pages are filled with detailed 

 geological sections, explained by an abbreviated notation that is not always easily interpreted ; 

 but intercalated among these are many items of special interest. An Inoceramus was found 

 that measured 43 inches across; a worthy rival of the giant Tridacna in the South Seas of to-day. 

 "Witch pinnacles," or slender columns of weak gravels capped by large bowlders, were figured 

 as occurring on the retreating eastern slope of the Kaiparowits Plateau, and a curious note 

 follows a near-by sketch of several of them : 



Opposite the point we climb is a red pinnacle 5 m. out in the valley as slender & as inclined & probably 

 on as large a scale as the tower of Pisa. 



