1902.] DAVIS— SYSTEMATIC GEOGRAPHY. 245 



explanatory treatment. Geographers have been slow to accept this 

 responsibility. True, they have long explained volcanoes by 

 eruption, because Eruptions have been witnessed ; yet they have 

 been habitually inattentive to the radial gorges by which extinct 

 volcanoes are scored. While gorges and water-gaps are still some- 

 times ascribed to fractures and floods, most geographers of a fair 

 degree of training explain them more wisely as the result of slow 

 sawing by the streams that flow through them ; yet most geograph- 

 ers are still accustomed to adducing a canyon and not a peneplain 

 in evidence of the magnitude of the work that can be done by rain 

 and rivers. There is therefore no more wholesome discipline for 

 the field geographer than to insist on the necessity of explaining 

 every part of the land form that comes under his observation. His 

 courage in this respect should be whole-souled rather than half- 

 hearted ; and whatever difficulties he may encounter, the success 

 already attained should strengthen his resolution to pursue his task 

 until complete success is reached. 



9. Explanation involves Past History. — It is evident however 

 that an explanatory method of description involves the considera- 

 tion of the past history through which land forms have come for- 

 ward to their present estate ; and thus the subject of physiography 

 gains a strong savor of geological methods. Some geographers 

 seem to be disconcerted by this consequence of the explanatory 

 treatment. They appear to think that description through pro- 

 cesses of origin involves too serious a trespass on the field of 

 geology, and they therefore give explanation over to the geologist. 

 But there is nothing novel in the trespass of one science upon the 

 methods of another. The chemist is constantly employing physical 

 methods \ the astronomer is as constantly employing mathematical 

 and physical methods. Hence no apology is needed if the geog- 

 rapher employs geological methods whenever they serve his pur- 

 pose. The real point is that these geological methods serve a 

 geographical purpose ; the purpose, namely, of aiding the observa- 

 tion and description of land forms, for which the geographer is 

 primarily responsible. Any methods that aid this end are ap- 

 propriate. Much attention as the geographer may give to pro- 

 cess and time as involved in the sculpture of land forms, 

 his interest in these geological elements is not aroused simply 

 from the hope of tracing out the sequence of events that the 

 past contains, but from the expectation, well warranted by abun- 



