184 



SCIENCE. 



[N. S. Vol. XIX. No. 474. 



ciers do not erode, the valley systems of 

 once glaciated mountains ought not to ex- 

 hibit any significant peculiarity of form, 

 but should correspond to the normal 

 stream-worn valley systems of non-gla- 

 ciated mountains. On the supposition that 

 glaciers do erode, the valley systems of 

 once glaciated mountains should exhibit 

 the highly specialized feature of a discord- 

 ant junction of branch and trunk; for the 

 channels eroded by a small branch glacier 

 and by a large trunk glacier must stand 

 at discordant levels at their junction, just 

 as the channels of a small stream and a 

 large river do, though the measure of dis- 

 cordance is much greater in the channels 

 of the clumsy, slow-moving ice-streams 

 than in the channels of the nimble, quick- 

 moving water-streams. There can be no 

 question that these well-specialized conse- 

 quences, deduced from the postulate that 

 glaciers can erode their channels, are much 

 more accordant with the actual features of 

 valley systems in once glaciated mountains 

 than are the consequences deduced from 

 the opposite postulate; but my reason for 

 introducing this problem here is not to 

 call attention to the value of ' hanging 

 valleys ' in evidence of glacial erosion, as 

 first clearly set forth by Gannett in 1898" 

 in his account of Lake Chelan, but rather 

 to poiiit out how slow geographers have 

 been to employ the deductive method in 

 solving this long-vexed problem. The 

 moral of this is that geographers as well as 

 geologists, physicists, astronomers, ought to 

 have good training in scientific methods of 

 investigation, in which all their faculties 

 are employed in striving to reach the goal 

 of full understanding, instead of depend- 

 ing so largely on the single faculty of ob- 

 servation. 



Some may, however, object that the 

 problem of glacial erosion, just touched 

 upon, belongs exclusively to geology, and 

 not at all to geography. It belongs to 



both ; its association will be determined by 

 its application, as the following considera- 

 tions will show. The accumulation of 

 sand-dunes by wind action, the abrasion 

 of sea-coasts by waves, the erosion of 

 gorges by streams, the construction of vol- 

 canoes by eruptions now in progress, man- 

 ifestly belong in the study of physical 

 geography, in close association with the 

 blowing of the winds, the rolling of the 

 waves, the flowing of streams, and the out- 

 bursting of lavas and gases. Both the 

 agent and the result of its action are ele- 

 ments of the environment by which life is 

 conditioned. Similarly, the grass-covered 

 dunes of Hungary, the elevated sea-cliffs 

 of Scotland, the abandoned gorges of cen- 

 tral New Tork, and the quiescent volcanoes 

 of central France, are all elements of land 

 forms and are all treated as geographical 

 topics and explained by reference to their 

 extinct causes in the modern rational 

 method of geographical study. Likewise 

 the discordant valley systems of glaciated 

 mountains are proper subjects for explan- 

 atory treatment in the study of geography, 

 -although the glacier systems that eroded 

 them are extinct ; they deserve explanatory 

 treatment in geography just as fully as do 

 the accordant valley systems of non-gla- 

 ciated mountains. It is true that discus- 

 sion as to whether certain sculptured land 

 forms are due to glacial erosion is likely 

 to continue more or less actively through 

 the present decade ; but when this problem 

 is as well settled as the problem of stream, 

 erosion has already been, the geographer 

 will be content with the simplest statement 

 of the evidence that is essential to the con- 

 clusion reached; and the explanatory de- 

 scriptions of land forms will include due 

 reference to forms of glacial origin, just as 

 much as a matter of course as they now in- 

 clude reference to forms of marine or of 

 subaerial origin. Forms of glacial sculp- 

 ture will be given as assiired a place in 



