214 Dr. N. 0. Hoist— The Glacial Period and 



by breccia-formation, may be observed ia Scandinavia at many points 

 on the boundary-line between the Archgean and Cambro-Siluriaa 

 deposits, as on Bornholm, in Scania, on Lake Vetter, in Ostrogothia, 

 Nerike, Dalecarlia, Gestrikland, Jemtland, on the Christiania fjord, 

 on the Kola peninsula, and other places.^ Even the quite insignificant 

 occurrence of Silurian at Humlenas in the province of Kalmar can 

 show a similar fault with accompanying breccia-formation. For 

 my part I do not think that any explanation of these phenomena 

 will ever be found more satisfactory than that the earth's crust, 

 which during the Cambro-Silurian periods was much thinner than 

 now, yielded beneath the weight of the Cambro-Silurian sediments. 

 If such were the conditions, we can also understand the immense 

 thickness which the Palasozoic rocks occasionally attain, and which 

 may have arisen by the gradual sinking of the sea-floor in proportion 

 as the formation of sediment proceeded.^ 



But if sedimentation tends to depress the earth's crust, and 

 actually has depressed it in certain places, then to such a sinking 

 there must have corresponded elevation in another place ^ ; and it 

 is precisely this elevation above all that has affected the Archaaan 

 areas, and particularly the greater ones — those that could, so to 

 speak, move independently — because these areas have not merely 

 formed the thinnest parts of the crust, but have lacked the 

 strengthening influence of the stratified deposits. 



This, then, seems to have been the way in which elevation of the 

 Scandinavian and North American Archsean areas was brought 

 about and carried on, until at the beginning of the Glacial Period 

 they had reached such a height that each formed the centre for an 

 ice-sheet. 



If the conception put forward in the preceding pages is the right 

 one, it follows that the phenomena which accompany the appearance 

 of an ice-sheet involve such radical and manifold changes within 

 the glaciated area that an Ice Age cannot, so to say, come and go 

 unmarked, but must leave the most obvious traces behind it. 

 Therefore it is that the idea here propounded is utterly opposed to 

 the interglacialist view, and therefore it has been attacked by 

 champions of the latter.^ The chief objection raised by them to the 

 present explanation of the Ice Age is the following. 



Granted, they say, that this might be quite a satisfactory 

 explanation of the Scandinavian,- Greenland, and North American 

 ice-sheets, still it is not enough to explain the former small glaciated 

 areas in the Pyrenees, the Alps, the Caucasus, and so forth. To 



^ See " Generalregister" to vols, vi-x of Geol. Foren. Stockholm Forhaudl., p. 34. 



A fault in Jemtland is described by A. Hogbom in his paper, " Om forkastnings- 

 Dreccior vid den Jemtlandska sUurformationens ostra grans" : Geol. Foren. Stock- 

 holm Forhandl., 1886, viii, p. 352. 



The Palaeozoic faults on the Kola peninsula have been described by "W. Ramsay, 

 Fennia xvi, No. 1, pp. 2 and xv ; No. 4, pp. 7 and 11. 



^ The same views were expressed by James Hall in the "Palaeontology of New 

 York," iii, pp. 69 et sqq. ; Albany, 1859. 



3 Cf. J. Hall, op. cit., p. 95. 



" J. Geikie: "The Great Ice Age," 3rd ed., p. 792 ; London, 1894. 



