38 GROVE KARL GILBERT— DAVIS [ ^ EiIolRS [xo^xxi, 



What a leap earth science would have made at the end of the eighteenth century if this 

 founder of the uniformitarian school could have seen the plateaus of northern Arizona? 



There was, however, no lack of opportunity for the application of Hutton 's physiographic 

 principle in various well-known parts of the Old World. Northeastern France is unparalleled 

 as a field for the study of those unsymmetrical ridges, which are coming to be known as cuestas, 

 "sloping on the one side, and having a precipice on the upper part of the other side," because 

 they are developed on a series of gently inclined strata; yet although these cuestas have long 

 been familiarly known in their geological relations, they have been rarely studied physio- 

 graphically, perhaps by very reason of their familiarity. England also affords excellent and 

 early known examples of the relation between structure and form in the cuestas that traverse 

 its southeastern half, to say nothing of such striking though small features as the typically 

 Alleghenian zigzag by which the ridge known as the "Wenlock Edere" in Shropshire is offset 

 and extended south westward past Ludlow near the Welsh border; but with the development 

 of geological specialists, first in stratigraphy and paleontology and later in petrography, the 

 close examination of small rock outcrops that these sciences demanded seems to have distracted 

 attention from a broad grasp of the plant-covered landscape in which the structures, fractionally 

 disclosed in the outcrops, are often generalized. As to English geographers, they were indifferent 

 to geology through most of the nineteenth century and treated cuestas and other physiographic 

 features empirically if at all. It is true that Lyell ably applied and extended through the middle 

 of the nineteenth century the principles of uniformitarian geology that Hutton had established 

 at the end of the century before, but Hutton's beginnings in rational physiography had no 

 equally eminent exponent to carry them forward; witness the slowness of British geographers 

 to recognize the chalk escarpments around the Weald in southeastern England as cliffs of 

 subaerial denudation, not of marine abrasion; witness also their failure to describe the beautiful 

 and familiar embayments of Cornwall on the Atlantic coast of British Europe as partly submerged 

 valleys, until after this simple explanation for such features had been applied by Dana, as a 

 member of the United States exploring expedition under Wilkes, to the far-away Pacific 

 coast of British America. 



During the same period in the New World, the influence of the New York survey under 

 the leadership of Hall was dominantly stratigraphic and paleontologic ; and even the brilliant 

 correlation of structure and form established for the Alleghenies of Pennsylvania by Rogers 

 and Leslie had, in their time, no extended application elsewhere; perhaps because it was not 

 accompanied by a sufficiently rational treatment of deformational and erosional processes. 

 It was not until the West was penetrated that, in the absence of heavy vegetation, the relation 

 of surface form and underground structure, manifest for miles around in every extended view, 

 came to be understood as the systematical result of erosional processes acting slowly and 

 persistently through long-lasting time; and by none of the western explorers was this relation 

 more helpfully explained than by Gilbert. Apart from his views on the origin of the basin 

 ranges, it was in this physiographic field that his early contributions to earth science showed 

 the most originality. 



Gilbert 's physiographic work naturally found its best opportunity in the treeless parts of 

 plateau province, where the sequence from simple to moderately complicated structures is 

 so clear, where the apphcation of erosional processes in the production of surface forms is so 

 immediately visible, and where the change of eroded form with the change of structure and the 

 passage of time is so convincingly manifest. The rational treatment of land forms, already 

 begun elsewhere, here progressed rapidly; and the results to which such treatment soon led are 

 now so widely accepted under the evolutionary philosophy by which modern geography is like 

 other sciences dominated, that the present generation of geologists and geographers may find 

 it difficult to realize how large a share of the fundamental principles on which the physiography 

 of the lands has grown and flourished were implied or outlined or formulated no longer ago 

 than in Gilbert's first report. Young as he then was, he was either abreast or ahead of the 

 earth science of the time. 



