“I do not think that a description of the earth, which commences by telling a child that it is an oblate spheriod, moving around the sun in an elliptical orbit, and ends without giving him the slightest hint towards an understanding of the ordnance map of his own country, or any suggestion as to the meaning of the phenomena offered by the brook which runs through his village, or of the gravel pit whence the roads are mended, is calculated either to interest or to instruct.... Physiography has very little to do with this sort of Physical Geography. My hearers were not troubled with much about latitudes and longitudes, the heights of mountains, depths of seas, or the geographical distribution of kangaroos or Compositae.... I endeavored to give them ... a view of the ‘place in nature’ of a particular district of England—the basin of the Thames—and to leave upon their minds the impression that the muddy waters of our metropolitan river, the hills between which it flows, the breezes which blow over it, are not isolated phenomena, to be taken as understood because they are familiar. On the contrary, I endeavored to show that the application of the plainest and simplest processes of reasoning to any one of these phenomena suffices to show, lying behind it, a cause, which again suggests another; until, step by step, the conviction dawns upon the learner that, to attain to even an elementary conception of what goes on in his own parish, he must know something about the universe; that the pebble he kicks aside would not be what it is and where it is, unless a particular chapter of the earth’s history, finished untold ages ago, had been exactly what it was.... Many highly valuable compendia of Physical Geography, for the use of scientific students of that subject, are extant; but in my judgment most of the elementary works I have seen begin at the wrong end, and too often terminate in an ominum gatherum of scraps of all sorts of undigested and unconnected information; thereby entirely destroying the educational value of that study which Kant justly termed the ‘propædeutic of natural knowledge.’” (Preface to ‘Physiography,’ 1878).
Here we find clear recognition of the need of introducing a consideration of causes, just as was urged by Guyot; and furthermore a recognition of the need of linking together in their natural relations all the items which together constitute the content of the subject. It may, however, be contended that the attempt to combine in a single course of study the elementary principles of chemistry and physics, of geology and astronomy, along with those of physical geography, is not practicable from an educational point of view; such a combination will not secure either the clear knowledge or the strong discipline that can be derived from systematic courses in two or three of these subjects, presented separately. Text-books like Hinman’s ‘Eclectic Physical Geography’ and Mill’s ‘Realm of Nature,’ in both of which a broad range of other than geographical subjects is covered, do not seem to-day to be in so much favor as those books which attend more closely to the true content of our subject. Indeed, with respect to physical geography, considered from the scientific and educational point of view, a report on College Entrance Requirements, recently published by our National Educational Association,[D] presents the best definition and outline of the subject that has yet appeared. It advises the omission of irrelevant matter, however interesting such matter may be in itself. The principles of physics and the succession of geological formations with their fossils, the classification and distribution of plants and animals must be taught elsewhere; but much profit may be had from terrestrial phenomena by which the principles of physics are illustrated, and from the consequences of past geological changes in determining present geographical conditions, and especially from the physiographic controls by which the distribution of organic forms is determined.
[D] Proceedings, 1899, 780–792; also in the Journal of School Geography, September, 1898.
The general scheme under which all land forms may receive explanatory description must consider chiefly the movement and erosion of the earth’s crust. Deformation offers a part of the earth’s crust to be worked upon. Various destructive processes of erosion work upon the offered mass, and the streams, with their transported waste, follow the depressions in the carved surface. So important is the element of erosion, and so leading is the part played by rivers in erosive work, that McGee would gather all land forms under a classification determined by their drainage systems.[E] Others have preferred a classification based, first on peculiarities of structure as determined by accumulation and deformation; and, secondly, on the progress of erosion; but in either scheme, the erosive work of rivers is so important that a sketch of the progress of the physical geography of the lands towards a systematic classification of its items may well follow the order in which valleys have been explained, branching off, as occasion may require, from the leading theme of rivers that flow under a normal humid climate to special conditions of erosion under an arid or a frigid climate. The progress which has made the physical geography of the lands what it is to-day is more the work of geologists than of geographers; and the chief reason for this is the indifference of many geographers to the physical side of their subject; an indifference that was undoubtedly favored by the cultivation of historical geography in continental Europe, and by the acceptance of the traveler or explorer as a full-fledged geographer in Great Britain. In the United States, it is only in the latter part of the century that the physical geography of the lands has gained a scientific standing, and the advantages that it now enjoys are geographical grafts upon a geological stock.
[E] Nat. Geogr. Magazine, i, 1889, 27–36.
The emancipation of geology from the doctrine of catastrophism was a necessary step before progress could be made towards an understanding of the lands. The slow movements of elevation and depression of certain coasts in historic time were of great importance in this connection. Studies of geological structures at last overcame the belief in the sudden and violent upheaval of mountain chains, which, under the able and authoritative advocacy of Elie de Beaumont, held a place even into the second half of the century. But even when it came to be understood that mountains and plateaus have been slowly upheaved, it still remained to be proved that the valleys and canyons by which they are drained were produced by erosion, and not by fractures and unequal movements of elevation. Advance was here made on two lines. Along one, a better understanding was gained of the forms producible by deformation alone; along the other, sea currents, floods and earthquake waves, to which the earlier observers trusted as a means of modifying the forms of uplift, were gradually replaced by the slow action of weather and water. Processes of deformation were found to act in a large way, producing massive forms without detail—broad plains and plateaus, extensive domes, straight cliffs and rolling corrugations; and thus it was learned that the varied and detailed forms of lofty mountain ranges and dissected plateaus must be ascribed almost entirely to the processes of erosion. But it should be noted that in exceptional instances land forms initiated by deformation, so recently as to have suffered as yet only insignificant sculpture, may exhibit much irregularity. The most striking example of this kind, an example of the very highest value in the systematic study of land forms, is that afforded by the diversely tilted lava blocks of Southern Oregon, as described by Russell.[F]
[F] 4th Ann. Rep. U. S. Geol. Survey, 1883.
Turning now to the second line of advance, it is noteworthy that so keen an observer as Lesley insisted, as late as 1856, that the peculiar topographical features of Pennsylvania, which he knew and described so well, could have been produced only by a great flood. But the principles of the uniformitarians were constantly gaining ground against these older ideas; and after the appearance in England of Scrope’s studies in Central France and of Greenwood’s polemic little work on ‘Rain and Rivers’ (1857), victory may be said to have been declared for the principles long before announced by Hutton and Playfair, which, since then, have obtained general acceptance and application.
Yet even the most ardent uniformitarians would, in the middle of the century, go no further than to admit that rain and rivers could roughen a region by carving valleys in it; no consideration was then given to the possibility that, with longer and longer time, the hills must be more and more consumed, the valleys must grow wider and wider open, until, however high and uneven the initial surface may have been, it must at last be reduced to a lowland of small relief. The surface of such a lowland would truncate the underground structures indifferently; but when such truncating surfaces were noticed (usually now at considerable altitudes above sea level, as if elevated after having been planed, and therefore more or less consumed by the erosion of a new system of valleys), they were called plains of marine denudation by Ramsay (1847), or plains of marine abrasion by Richthofen (1882). Today it is recognized that both subaërial erosion and marine abrasion are theoretically competent to produce lowlands of denudation; the real question here at issue concerns the criteria by which the work of either agency can be recognized in particular instances. In the middle of the century, not only every plain of denudation, but every line of escarpments was held by the marinists to be the work of sea waves; and it was not till after a sharp debate that the bluffs of the chalk downs which enclose the Weald of southeastern England were accepted as the product of ordinary atmospheric weathering, instead of as the work of the sea. Whitaker’s admirable essay on ‘Subaërial Denudation,’ which may be regarded as having given the victory in this discussion to the subaërialists, was considered so heterodox that it was not acceptable for publication in the Quarterly Journal of the Geological Society, of London, but had to find a place in the more modest Geological Magazine (1867), whose pages it now honors. So signal indeed was this victory that, in later years, the destructive work of the sea has been not infrequently underrated in the almost exclusive attention given to land sculpture by subaërial agencies. Truly, the sea does not erode valleys; it does not wear out narrow lowlands of irregular form between enclosing uplands, as was maintained by some of the most pronounced marinists in the middle of the century; but it certainly does attack continental borders in a most vigorous fashion, and many are the littoral forms that must be ascribed to its work, as may be learned from Richthofen’s admirable ‘Führer für Forschungsreisende’ (1886). As this problem can not be further considered here, the reader may be at once referred to the most general discussion of the subject that has yet appeared, in an essay on ‘Shoreline Topography’ recently published by F. P. Gulliver.[G]
[G] Proc. Amer. Acad., Boston, 1899, 152–258.