114 W. M. DAVIS RELATION OF GEOGRAPHY TO GEOLOGY 



colonizers would have been killed or driven out and never had a chance to 

 return. True, when a beginner in geography first meets the word volcano 

 and learns likely enough that it is a burning mountain he gains no very 

 full understanding of all these dramatic changes, Just as when he first 

 studies history he gains no real appreciation of all the long continued 

 oppressions and struggles that eventually culminate in the outburst of a 

 revolution, of which he learns hardly more than the date. But does vol- 

 cano truly mean anything less than all the complication of events that is 

 here briefly sketched? Must not a mature and thoughtful geographer 

 strive when he says "volcano" to visualize the long succession of active 

 eruptions and quiescent periods, of upbuildings and downwearings, of 

 organic destructions and recolonizations which the single word, volcano, 

 implies ; must he not conceive all this long succession through which alone 

 he can come to know what the existing volcano really is ? And just in the 

 same way must not the mature historian go far beyond the schoolboy in 

 conjuring up slow-moving pictures of the past when he speaks of a revo- 

 lution, if he wishes to know what the revolution really was ? 



It is the same with the brief phrase, "a mature river." There was a 

 time not very long ago when a river with a maturely graded course could 

 be regarded, even by mature geographers, as simply an existing thing 

 without their feeling any concern about the long series of changes which 

 must inevitably have run their course before maturity could be reached; 

 but that time is not ours. I^o modern geographer who recognizes the 

 evolution of the present from the past — and no modern geographer can 

 fail to do that — no modern geographer can escape from imagining the 

 young stages of a river as preceding the mature in order properly to 

 appreciate the mature stages. Still more, if one speaks in concise terms 

 of "a meandering valley maturely incised in an uplifted peneplain of dis- 

 ordered structure," must the appreciative understanding of this descrip- 

 tive phrase build up the conception of the present on a long succession of 

 past events, and indeed not only on a succession of inorganic events, but 

 of organic events as well; for, as Woodworth first pointed out and as 

 Cowles has later so fully shown, there is a most intimate, systematic, and 

 essential correlation between these inorganic changes and the organic 

 changes that lead up to the present organic population of an uplifted 

 peneplain of disordered structure, traversed by an incised meandering 

 valley, and no proper account of the present populations can be given 

 without an appreciation of their past. Yet surely a geographer who 

 understands the abundant implications of the term volcano may use it 

 without being considered as encroaching on geological grounds, and he 

 may even speak of an uplifted peneplain traversed by an incised mean- 



