i82 The American Geologist. ^avi^h. 1904. 
Some may, however, object that the problem of glacial ero- 
sion, 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 consider- 
ations will show. The accumulation of sand-dtmes by wind 
action, the abrasion of sea-coasts by waves, the erosion of 
gorges by streams, the construction of volcanoes by eruptions 
now in progress, manifestly 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 elements of the environment by which life is con- 
ditioned. Similarly, the grass-covered dunes of Hungary, the 
elevated sea-cliffs of Scotland, the abandoned gorges of central 
New York, 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 explanatory treatment in the study of geography, 
although the glacier systems that eroded them are extinct ; they 
deserve explanatory treatment in geography as fully as do the 
accordant valley systems of non-glaciated mountains. It is true 
that discussion as to whether certain sculptured land forms are 
due to glacial erosion is likely to continue more or less active- 
ly 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 conclusion reached ; and the 
explanatory descriptions of land forms will include due refer- 
ence to forms of glacial origin, just as much as a matter of 
course as thev now include reference to forms of marine or of 
subaerial origin. Forms of glacial sculpture will be given as 
assured a place in geographical study as forms of glacial de- 
position are already given. Neither the thing studied, nor 
the agent by which it was produced, nor the method by which 
the agent is shown to be accountable for the thing, suffices to 
show whether the thing is of a geological or a geographical 
nature. This question will be decided, as has already been 
shown, h\ the relations into which the thing enters. It would 
