THE PHYSICAL GEOGRAPHY OF THE LANDS. 163 



work, that Mcliee would gather all laud forms under a classification 

 determined by their drainage systems.* Others have preferred a classi- 

 fication based, first on peculiarities of structure as determined by accu- 

 mulation 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. 



The emancipation of geology from the doctrine of catastrophism 

 was a necessary step before progress could be made towards an under- 

 standing of the lands. The slow movements of elevation and depres- 

 sion 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 corru- 

 gations; 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 



* Xat. Geogr. Magazine, i, 1889, 27-36. 



