112 P. A. ØYEN [1914 



period of valley glaciation« (L. c. pag. 152). Men i disse af 

 isen dannede og af bræerne omformede dale, finder vi som paa 

 andet sted omtalt, enten ofte en gjentat daldannelse, eller vi 

 finder daltrin, eller vi finder, som af amerikanske geologer frem- 

 hævet »hanging lateral valley s and overdeepened main valley s« 

 (^Davis: »Glacial erosion in France, Swilzerland and Norway « — 

 Proceed. Boston Soc. Nat. History, Vol. 29, Nr. 14, 1900, pag. 

 273 — 322). ■ Alle disse former ordner sig paa en helt lovmæssig 

 maate, der viser en lovmæssig utvikling og er godt formet i 

 Dalys uttalelse: »the evidences for the existence of any general 

 peneplain over the Cascades at any time in the history of the 

 system seem extremely weak (L. c. pag. 627), og han resumerer 

 videre resultaterne af sine undersøkelser i følgende: »The form 

 of the preceding discussion has been analytical, but its main 

 point has been to emphasize the synthetic nature of the process 

 of mountain sculpture. Seven different conditions of erosion work 

 together to produce accordance of summit levels in an ideal 

 alpine range undergoing its first cycle of physiographic devel- 

 opment. Isostatic adjustment and simultaneous, differential 

 degradation of rising blocks tend to bring about rough accor- 

 dance of summit levels in the range as »originally« formed. 

 Later differential erosion and consequent further isostatic ad- 

 justment, the influence of metamorphism and intrusion, the 

 sculpture due to high-level glaciation, the normal existence of a 

 high-level tree-line, and, finally, the compound process of river 

 spacing and slope gradation — alt these may combine their 

 effects and render more perfect the accordance of levels inheri- 

 ted from the early, growing period of the range. This compo- 

 site explanation must, therefore, be considered very carefuUy 

 in discussing the origin of the present relief in an alpine range 

 where there are no remnant plateaus directly referable to a 

 common, uplifted and dissected peneplain. Such accordance 

 may give a comparatively even sky-line in views from any 

 dominating point, but the full force of the composite explana- 

 tion is directed against the reference of that even sky-line to 

 the direct or inherited profila of a peneplained surface«. (Daly: 

 Geology of the North American Cordillera at the Forty-Ninth 

 Parallel, P. II, 1912, pag. 641). 



Naar vi ser hen til den rolle, amerikanske forskere har hat 

 med hensjm til utviklingen af vort kjendskab til omformningen 

 af jordklotens overflate, vil det kanske heller ikke, skjønt det 

 til at begynde med lyder noget fjerntliggende, høres saa underhg, 

 at det netop var en amerikansk forsker, som først systematisk 

 bearbeidede, inden et mere begrænset strøk, til og med delvis 

 inden vort foreliggende omraade, en ny gren af overflateforsk- 



