I l6 GILBERT 



general hypothesis as to the cause of those local upliftings of 

 the earth's crust which make continents and mountains. He 

 announced the fundamental principles of control in the sculpture 

 of the land, crystallizing his central idea in the new term base- 

 level. He introduced a group of explanations of the relations 

 of waterways to mountains and ridges, accompanying the new 

 ideas with three new terms — consequent valleys^ antecedent val- 

 leys^ and superimposed valleys. 



None of these contributions to geologic philosophy was elab- 

 orated or adequately illustrated ; his presentation gave no sug- 

 gestion of the breadth of the inductions on which they were 

 founded. It was his belief that a scientific fact needed no argu- 

 ment, but only statement. The fruits of his study were cast 

 forth as simple seeds, to germinate or perish, according to their 

 worthiness or unworthiness, or as the accident of their environ- 

 ment might determine. The theory of mountain growth, the 

 last of the group to be announced, rests as he left it, and has 

 not yet demonstrated its vitality by growth. But the ideas 

 embodied in base-level, consequent, antecedent, and superimposed 

 fell on fertile ground, and have had a marvelous development. 

 A half score of younger men have elaborated, extended, and 

 applied them ; and they stand today for a division of the science 

 so important that it is sometimes called the ' new geology.' 

 Geologists and geographers now recognize that each hill, hollow, 

 and plain of the earth's surface originated by some process of 

 change, and is therefore susceptible of explanation and interpre- 

 tation. Whereas geologic history was formerly read in the 

 rocks alone, it is now read not only in the rocks but in the forms 

 of the land and the arrangement of the streams. 



Powell's contribution to applied geology involved much more 

 than the utilization of geologic knowledge. He dealt with the 

 complex problem of the subjugation to human use of 'the arid 

 portion of our national domain, and he brought to bear on 

 it the scientific data of climatology and sociology as well as 

 geology. His Lands of the Arid Region, published nearly 

 twenty four years ago, set forth with marvelous insight the 

 conditions by which the problem is surrounded, and formu- 

 lated the principles by which much of the later work has been 



