1 1 2 P. A. ØY KN [1914 



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

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

 andel sled omtall, enlen ofte en gjenlat daldannelse, eller vi 

 linder dallrin, eller vi linder, som al" anieiikanske geologer frem- 

 hævet lianging laleral valleys and overdeepened main valleys« 

 iDavis: »(ilacial erosion in 1^'rance, Swilzerland and Norway« — 

 Proceed. Hoston Soc. Nat. Hislory, Vol. 29, Nr. 14, 1900,"^ pag. 

 273 — 822). Alle disse former ordner sig jiaa en heil lovmæssig 

 maale, der viser en lovmæssig ulvikling og er godl formel i 

 Daly's ullalelso: the evidences for Ihe exislence of any general 

 peneplain over the (>ascades at any lime in the history of the 

 system seein extremely weak (L. c. pag. G27), og han resumerer 

 videre resultaterne af sine undcrsøkelser i følgende: »The form 

 of the precoding discussion has heen analytical, but ils main 

 point has Ixhmi to emphasize the synthetic nature of the process 

 of mountain scnlpture. Seven dilVerent conditions of erosion work 

 together lo produce accordance of summil levels in an ideal 

 al|)ine range undergoing ils lirsl cycle of physiographic devel- 

 opmenl. Isostatic adjustment and simullaneous, dilVerential 

 degradation of rising hlocks lend to bring aboul rough accor- 

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

 Laler diHerenlial erosion and consetjuent furlher isostatic ad- 

 justment, the inlluence of melamorphism and inlrusion, the 

 sculplure due lo high level glacialion, the normal exislence of a 

 high level tree-Iine, and, linally, the compound process of river 

 sjjacing and slope gradation — alt these may combine their 

 effects and render more perfecl Ihe accordance of levels inheri- 

 ted from Ihe early, growing period of the range. This comj)o 

 sile explanalion must, therefore, be considered very carefuUy 

 in discussing Ihe origin of the i)resent relief in an alpine range 

 where Ihere are no remnanl plateaus directly referable lo a 

 common, uplifled and dissected penei)lain. Such accordance 

 may give a c()iu|)ara lively even sky-line in views from any 

 dominaliug point, bul the full force of Ihe composile explana 

 lion is direcled againsl Ihe reference of thai even sky-line lo 

 the direcl or inheiited prolile of a peneplained surface«. (Dalv: 

 Geologv of Ihe North American Cordillera at the Forty-Ninth 

 Parallel, P. II, 1912, pag. (i41). 



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

 med hensyn til ulviklingen af vort kjendskab til omformningen 

 af jordklolens overllate, vil det kanske heller ikke, skjønl del 

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

 al del netop var en amerikansk forsker, som først syslemalisk 

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

 inden vort foreliggende omraade, en ny gren af overflaleforsk- 



