CHAPTER V 

 PHYSIOGRAPHY IN THE WHEELER REPORTS 



THE GRADUAL GROWTH OF PHYSIOGRAPHY 



It has often been remarked that the early geological explorers of the West were impelled 

 to consider surface forms in close association with underground structures because of the mani- 

 fest relations of the two in a treeless region. This was never truer than in Gilbert's case. He 

 does not appear ever to have had any teaching in physical geography; and indeed, even if he 

 had, the subject as it was taught in his boyhood and youth, 60 years ago, would have given him 

 little or no understanding of the causal connection between the rock structures beneath the 

 surface forms and the surface forms of the rock structures. Furthermore, his two years' ex- 

 perience on the drift plain of northwestern Ohio can not have helped him much to learn the 

 dependence of form on structure, although his keen power of observation and his analytical 

 turn of mind did enable him to gain an understanding of certain surface features in that dis- 

 trict of faint relief, as has been told above. But his three seasons in the West made him a 

 physiographer. 



It is curious to recall, when one reviews the relations between geology and physical geog- 

 raphy for something more than a century past, how promising a beginning of close association 

 between the two sciences was made, when both were young, by Hutton in his Theory of the 

 Earth; how far apart they drifted 50 years later when geology, as it seasoned and matured, 

 nevertheless became largely the science of the crustal structure and history, while physical 

 geography was stagnating in empiricism; and how intimately the two rejoined each other after 

 the exploration of the West began. For geology, then recognizing that it must attend to the 

 surface of the earth as well as to its under structure, gave new life to the physical geography of 

 the lands, and this vivifying influence was happily applied at about the same time that the 

 doctrine of evolution enlivened and invigorated all aspects of organic geography. It is gratify- 

 ing to see how largely Gilbert's western work contributed to the extension of the physiographic 

 line of geological investigation into the rich but little cultivated field of the geography of land 

 forms. 



Hutton was a leader among those who, 130 years ago, at the beginning of the association 

 between geology and geography, set forth in very simple terms certain relations between struc- 

 ture, erosion, and form. Had the foundation then laid been continuously built upon, the 

 physiography of the lands would not have been so modern a science as is actually the case. 

 The old master pointed out that, in various mountain forms, 



we find the original structure of the mass influencing the present shape in conjunction with the destructive 

 causes. . . . Now, this original shape is no other than that of beds or strata of solid resisting rock, which may 

 be regularly disposed in a mountain, either horizontally, vertically, or in an inclined position; and those solid 

 beds may then affect the shape of the mountain in some regular or distinguishable manner. . . . Thus, a hori- 

 zontal bed of rock forms a table mountain. . . . An inclined rock of this kind forms a mountain sloping on the 

 one side, and having a precipice on the upper part of the other side, with a slope of fallen earth at the bot- 

 tom. . . . Wereitvertical, again, itwouldformarockyridgeextendedinlength.andhavingitssidesequally sloped' 

 so far as the other circumstances of the place would permit. Therefore, whether we suppose the mountain 

 formed of a rock in mass, or in that of regular beds, this must have an influence in the form of this decaying 

 surface of the earth, and may be distinguished in the shape of the mountains. 



The observant Scotch theorist was indeed so convinced of the truth of the principle that 

 form is dependent upon structure that he reversed it and inferred structure from form: 



In distinguishing, at a distance, those regular causes in the form of mountains, we may not be able to tell, 

 with certainty, what the substance is of which the mountain is composed, yet, with regard to the internal struc- 

 ture of that part of the earth, a person of knowledge and experience in the subject, may form a judgment in 

 which, for coming at truth, there is more than accident; there is even more than probable conjecture. 1 



' Theory of the Earth, Edinburgh, 1785; pages 411, 412, 413. 



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