632 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



number of alpine ranges. The accordance of summit altitudes has been noted 

 in the Alps, in parts of the Caucasus, in the Pyrenees, in the Sierra Nevada of 

 California, in the Alaskan ranges, in the Canadian Selkirks and Coast range, 

 and in the American Cascade range. We have seen that Willis regards the 

 accordance of summit levels in the Galton-MacDonald mountain system as an 

 indication of an uplifted mid-Tertiary peneplain. An illustration of the phenom- 

 enon is given in Plates 52, 66, 68, and 73 C. Views in other ranges traversed by 

 the Boundary belt are given in Plates 26, 28, and 45. 



The fact of accordance is established, while the theories of explanation are 

 very various. That they need critical examination and sifting is clear, not only 

 for the sake of the important fact of accordance itself, but also for the reason 

 that these theories involve widely diverging views on great physiographic 

 revolutions. Geological history in long chapters is thereby as expressly, implied 

 as it would be by the interpretation of purely stratigraphic evidences, illustrat- 

 ing over and over again the truth that both classes of evidences are required 

 in building up a complete history of the earth. Not only do these theories 

 involve premises regarding great denudations, but,, as well, a multitude of details 

 concerning river history and the evolution of individual mountain massifs. 

 There are likewise involved correlative views of the physiographic development 

 of the neighbouring regions, both on the large scale and in details. Geographic 

 description and nomenclature should be controlled by reference to the correct 

 theory or theories of land-form origins. Finally, large conclusions concerning 

 the origin of the force of mountain uplift must follow in the wake of certain 

 of the hypotheses already announced to explain the phenomenon of accordance 

 in summit levels. The attempt has even been made to connect the origin of 

 fractures and of mineral veins with the specialized kind of crustal movement 

 imagined for one explanation of this accordance.* There are thus abundant 

 reasons for coming to a wise decision as to the best explanation of the fact. 



The hypotheses dealing with this sympathetic attitude of alpine summits 

 may be classified on the basis of the logical explanation of an organism, 

 (a) How far is the feature in question due to inheritance? (b) How far is it 

 due to spontaneous development in the present environment? A review of the 

 hypotheses shows, everywhere and naturally, emphasis placed on erosion, but 

 the writer believes that the possibilities of inheritance are only partially worked 

 out, and, again, that the methods of spontaneous development are not yet 

 brought into the proper balance for final discussion or decision on the question. 



I. EXPLANATIONS BY INHERITANCE. 



1. Among the various explanations by inheritance we have, first, the 

 peneplain theory, which need not further be discussed in this place. 



2. Hypothesis of original rough accordance of summit levels, due to isosta- 

 tic adjustment. — Basal to all of the alternative hypotheses is the inquiry as to 



* A. C. Spencer. Transactions of the Amer. Institute of Mining Engineers, Oct., 

 1904. p. 35. 



