Triassie Formation of the Connecticut Valley. 431 



tion and slight changes of level. Like mountains of repeated 

 growth, this topography may be called " polygenetic." The 

 present form of the region ■ is modeled with reference to at 

 least two base-levels. 



Just as southern Idaho and central Nevada furnish illustra- 

 tion of the initial and somewhat advanced topographic forms 

 assumed in the development of our Connecticut district, so 

 there will doubtless be found somewhere on the earth, regions 

 of similar structure, presenting actual illustrations of its later 

 stages, when its stronger forms were subdued and finally worn 

 down to the featureless surface or peneplain of its old age. 

 Thus the evolution of the region will be better understood. 

 By this process of comparison,* we may not only restore in 

 some measure the past history of our region, but may as well 

 look into its possible future. When later elevation raises our 

 eastern continental slope to still greater altitude and exposes 

 the mass of the land to still deeper attack by erosive forces, 

 it may happen that the base-level will take such a position 

 as to allow the discovery of the ridges of fundamental crystal- 

 lines between the fault lines at the base of the Triassie trough ; 

 and this stage has its forerunner in a district of northern 

 China (Shantung), described by Bichthofen.f The structure 

 of the district is summarized as consisting of crystalline schists 

 of steep dip, unconformably overlain by Cambrian sediments ; 

 this compound mass is broken by a system of sub-parallel 

 faults running east or southeast, with upthrow on the southern 

 side, and with a tilting of the faulted blocks by which the 

 uncomformable cover of Cambrian sediments dips southward 

 toward the faults. The deformation is ancient, and subsequent 

 denudation has exposed the fundamental crystallines in long 

 narrow ridges, which by their superior hardness have become 

 water sheds (whether they have always been so or not does not 

 appear, as the successive cycles of river history from the first 

 to the present are not deciphered), while the Cambrian sedi- 

 ments remain in narrow monoclinal strips between every ridge 

 and the next fault to the south. The bottom of our Connec- 

 ticut trough may some day be worn into similar ridges and 

 valleys. 



* During the preparation of this paper, I have had pleasure in meeting evidence 

 of the value of the method here outlined in an essay by Dr. V. Hilber of Graz, 

 Austria In discussing the origin of cross-valleys, he suggests an inductive 

 illustration of their development, as follows : '• Auch eine Methode welche in der 

 vergleichende Erdkunde noch kaum Anwendung gefunden hat, welche aber auch 

 fur andre Fragen derselben berucksichtigenswert erscheint . . . . ist das Auf- 

 suchen derjenigen Oberflachenformen, welche als Entwickelungsstadien der vol- 

 lendeten Erscheinung betrachtet werden konnen." Die Bildung der Durchgangs- 

 thaler, Pet. Mitth , xxxv, 1889, 15. 



f China, II, 239, Fig. 56. See also Philippson, Studien iiber Wasserscheiden, 

 119. 



