Oeographic Methods in Geologic Investigation. lY 



wasting life of a single structure, reverse the conception and 

 we have a powerful geographic method for geologic investiga- 

 tion. On entering a new country, apply there the principles 

 learned from the inductive study of familiar regions, and much 

 past history is revealed ; the age of mountains may be deduced 

 from their form as well as from their rocks ; the altitudes at 

 which a district has stood may be determined by traces of its 

 old base levels, of which we learn nothing from the ordinary 

 routine of geologic observation, that is, from a study of the 

 structure and age of the rocks themselves. The principle is com^- 

 monly employed nowadays, but its methods are not formulated, 

 and its full value is hardly yet perceived. Heim has found traces 

 of successive elevations in the Alps, proved by incipient base 

 levels at several consistent altitudes on the valley slopes. New- 

 berry, Powell and Dutton have worked out the history of the 

 plateau and cailon region from its topography; Chamberlin and 

 Salisbury write of the young and old topographic forms of the 

 drift-covered and the driftless areas in Wisconsin ; LeConte and 

 Stephenson have interpreted chapters in the history of California 

 and Pennsylvania from the form of the valleys. Recently Mc- 

 Gee has added most interesting chapters to the history of our 

 middle Atlantic slope, in an essay that gives admirable practical 

 exposition of the geographic methods. In the light of these 

 original and suggestive studies one may contend that when 

 geographic forms in their vast variety are thus systematically 

 interpreted as the surface features of as many structures, belong- 

 ing to a moderate number of families and having expression 

 characteristic of their age and accidents, their elevation and 

 opportunity, then geography will be for the wasting Unds what 

 palaeontology has come to be for the growing ocean floors. 



An interesting compai'ison may be drawn here. Fossils were 

 first gathered and described as individual specimens, with no 

 comprehension of their relationships and their significance. It 

 was later found that the fossils in a certain small part of the 

 world, England — that wonderful epitome of geologic history — 

 were arranged in sequences in the bedded rocks containing them, 

 certain groups of forms together, successive groups in shelves, as 

 it were, one over another. Then it was discovered that the local 

 English scale had a wider application, and finally it has come to be 

 accepted as a standard, with certain modifications, for the whole 

 world. The exploring geologist does not now wait to learn if 

 3 



