Nr. 6] KVARTÆR-STUDIER I TRONDHJEMSFELTET 215 



har WooDWARD git en god oversigt i sin » Manual of the Mollusca« 

 (London 1910, pag. 54). Woodward anfører her, at Mr. Kirry 

 »regarded» de nævnte provinser »as fixed by the will of the 

 Creator, ralher than as regulated by isothermal lines«, og at 

 Mr. SwAixsoN har vist, at circumstances connected with tempera- 

 ture, food, situalion, and foes, are totally insufficient to account 

 for the phenomena of animal geography«, som han saa tilskriver 

 »operation of unknown laws«. Og Woodward sier, at »the most 

 important contribution towards a knowledge of these »unknown 

 laws has been made by Professor E. Forres s idet han ogsaa 

 videre tilføier: it may be stated that — — — the Faunas of 

 the Provinces are of various ages, and that their origin is con- 

 nected with former geological changes, and a different distributioii 

 of land and water over the surface of the globe«. Det var den 

 samme tanke, som paa en mere aarsaksmæssig og bestemt maate 

 blev videre utformet af Croll, der uttaler: »That a geographical 

 distribution of land and water permitting of the existence and 

 deflection of those heat-bearing currents is one of the main 

 factors in my theory is what must be obvious to every reader 

 of Climate and Time'. The difference between Mr. Wallace 

 and myself is this: — I maintain that with the present distri- 

 bution of land and water, without calling in the aid of any other 

 geographical conditions than now obtain, those physical agencies 

 detailed in 'Climate and Time' are perfectly sufficient to account 

 for all the phenomena of the Glacial Epoch, including those 



intercalated warm periods while Mr. Wallace, on the 



other hand, maintains that without assuming some change in 

 the geographical conditions of our globe those physical agencies 

 will not account for that state of things« (The American Journal 

 of Science, Ser. 3, Vol. 27 (1884), pag. 89). Og denne vekshng 

 foraarsaket ved klimatiske forandringer møter vi igjen overalt, 

 — fænomenet er det samme, naar George fremhæver, at »in 

 each glacier there are two loci of maximum erosion; one at 

 the head of the glacier — — — the other beneath the central 

 zone of the glacier itself some distance upstream from the foot 

 of the glacier (» Canada Geol. Surv. Memoir. No. 38, P. II, 1912, 

 pag. 636), og naar vi møter to og to af indsøer grupperet i de 

 bræskurede dale eller botner som et bevis for bræernes eroderende 

 betydning likeoverfor reliefets utformning og det tiltrods for, at 

 Davis, som senere har bidrat saa meget til at belyse glacial- 

 erosionens natur og betydning som reliefdannende faktor, i 1882 

 ganske kategorisk uttalte: No large lakes have been produced 

 by glacial erosion — — — the most considerable topographic 

 effect produced by glaciers ist the heaping of various morainal 

 deposits on an area smaller than their source < (Proc. Bost. Soc. 



