SUMMIT LEVELS AMONG ALPINE MOUNTAINS 109 



as due to inheritance, after mature erosion, from the initial pene- 

 plained surface with which the present physiographic cycle opened. 

 The sculpture of the unwarped surface is by some attributed largely 

 to streams definitely controlled in their direction of flow by the general 

 slopes of the warped peneplain, i. e., consequent streams. In the 

 Cascade Range of Washington, Messrs. Willis and Smith make the 

 special supposition of transverse up warps and down warps compli- 

 cating the initial form of the uplifted Pliocene peneplain from which 

 the present range is supposed to have "descended." Mr. Spencer 

 has deduced peneplanation and arch-warping for the Coast Range 

 of British Columbia. He is therewith compelled to place in a differ- 

 ent, antecedent, class a half-dozen of the chief rivers cutting clear 

 across the range. 1 Revived subsequent streams — that is, those 

 developed on weak rock-belts during peneplanation and incited to 

 still deeper cutting on those belts by the upwarping — must form a 

 third kind of corrasive agents. Following the upwarping, local and 

 general glaciation will still further greatly complicate the scheme of 

 drainage. 



One may feel but little doubt that the peneplain theory is sound 

 when applied to the more or less classic cases of the Appalachian 

 Piedmont, the New Jersey, New England, and Acadian plateaus, 

 the plateaus of the Rhine, of Bohemia, and of central France and 

 Brittany. In each one of these instances the already well-discussed 

 criteria of the uplifted and sculptured peneplain are apparently well 

 satisfied. Each region shows excellent examples of the remnant, 

 high-lying plateau flats truncating rocks of complex structures. 

 Often the criterion of adjusted drainage is admirably fulfilled. Where 

 glaciation has not disturbed the normal conditions, the plateau rem- 

 nants of the former lowland still bear the deep residual soils expected 

 on the theory. Finally, in none of these regions is the geological 

 history of adjacent physiographic provinces discordant with the 

 peneplain theory. 



If any one of the criteria can be taken as more positive than the 

 others, it is that of extensive plateau remnants of the peneplain sur- 

 face. Yet it is clear that even those remnants will lose their flat- 

 topped character with prolonged erosion. The perfectly mature 



1 Bulletin of the Geological Society 0} America, Vol. XIV (1903), p. 125. 



