ACADEMY OF SCIENCES] WHEELER SURVEY 27 



with respect to their contributions to geology and physiography, will be presented in this and 

 the following sections, not only because of the evidence that they give of the rapid development 

 of his life work, but also because of their importance in the history of geological science. 

 Undoubtedly the best known and most frequently quoted chapters of his reports concern the 

 mountain ranges in and near the Great Basin, to which he was the first to give the general 

 name, basin ranges; yet his discussion of the structure, history, and form of these mountains 

 was less complete than that of the plateaus next adjoining on the east, regarding which his 

 excellent descriptions and well certified conclusions have been less frequently cited. This 

 contrast appears to have a double explanation. Gilbert's conclusions regarding the plateaus 

 agreed essentially with those reached about the same time or later by Powell and Dutton, 

 whose fuller accounts, published in separate volumes, practically superseded his few and brief 

 chapters. On the other hand, his conclusions regarding the basin ranges traversed those 

 reached at about the same time by the geologists of the Fortieth Parallel survey, and therefore 

 became widely known as the subject of a prolonged controversy, which even to-day is not 

 settled to the satisfaction of all concerned. Gilbert's views on this question were highly 

 original, but their first presentation was unfortunately very incomplete. They will be examined 

 in a special section, after the geologic and physiographic problems of the plateau province 

 have been set forth. 



The chief geological topics treated in Gilbert's contributions to Volume III of the Wheeler 

 survey reports are: Stratified rocks, their sequence, thickness, composition, and fossils, with 

 some discussion of the conditions of the deposition, their horizontal variations, and their place 

 in. the geological series; volcanic rocks, their sequence and distribution; the structures pre- 

 vailing in each of the two physiographic provinces under examination, which show, first, that 

 the deformed rock masses of the basin ranges and their inferred strong displacement by in- 

 visible marginal faults contrast strongly with the prevailingly horizontal strata of the plateaus 

 which are but moderately disturbed by visible faults and flexures ; but which show also that the 

 more disturbed blocks in the northern part of the plateau province represent structural transi- 

 tions between the less disturbed plateaus farther south and the basin range province on the 

 west; in a word, that the plateau province exhibits embryonic stages of the deformation which 

 is more fully developed in the basin range province; processes of deformation, concerning which 

 occasional brief but significant suggestions are offered; certain chapters of historical geology; 

 the absence of general glaciation; erosional processes; and lacustrine records, chiefly those of 

 the great extinct lake to which Gilbert gave the name of Bonneville and on which he later 

 prepared a monograph, to be analyzed on a later page, as his chief publication under the United 

 States Geological Survey. Fuller statements concerning some of the above topics will be given 

 in the following sections, with page references to Volume III. 



Gilbert shared with Marvine and Howell the duty of coloring geologically eight of the 

 Wheeler survey topographical maps, prepared with hachures on a scale of 8 miles to an inch. 

 The area covered includes parts of Utah, Nevada, Arizona, and New Mexico, and the colors 

 distinguished eight time divisions and two groups of igneous rocks. Of course the geological 

 boundaries are broadly generalized and without detail. 



The chief physiographic results— that is, all discussions of land forms as dependent on rock 

 structures and surface agencies — will be summarized in later sections. They concern the forms 

 produced by stream erosion and by general degradation in plateaus of horizontal structure, 

 by the general erosion of volcanic cones and lava fields, and by the advanced denudation of 

 monoclinal flexures and upheaved domes; little attention was given to the description of forms 

 exhibited by the irregularly deformed structures of the basin ranges. Two general laws of 

 erosion were formulated and applied in a highly suggestive manner. The erosional reduction 

 of highlands or uplands to plains was clearly recognized, and the distinction is intimated between 

 the young forms of a later cycle of erosion introduced by the uplift of a region, and the old 

 forms that had been previously developed in an earlier cycle. 

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