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one which follows Suess, and a smaller one which considers the geo- 

 synclines as the fundamental feature of the framework of the earth. 



As is well known, Suess, following the suggestions of American 

 petrographers, divided the earth crust into three concentric divisions, 

 namely, the central Barysphere, which he termed the Nife (Ni-Fe) ; 

 the Sima (Si-Mg) ; and the Sal (Si-Al) . The latter two have been 

 united by Wiechert as the stone crust or lithosphere, the Sima corre- 

 sponding to the heavier basic, and the Sal to the lighter eruptive 

 rocks. The sedimentary envelope or " stratosphere " of Suess 

 is almost entirely formed at the expense of the Sal. While formerly 

 one sought to explain the anomalies of gravity by the assumption 

 of a thinner layer of the lithosphere above the barysphere, or a 

 " coming up " of the barysphere under the oceans (see Kayser, 19 13), 

 one is now inclined to consider the continents as lighter bodies, 

 consisting of Sal, that float upon and are partly imbedded into the 

 heavier Sima that also underlies the oceans (see Wegener and Andree) . 

 As it is recognized that there could not have been an exchange on 

 a large scale of these masses, the permanence of the oceans and con- 

 tinents is a corollary of this view. But it has also led to the hypothe- 

 sis of "horizontal continental displacements" of Wegener, according 

 to which the lighter continental masses have moved upon the heavier 

 Sima during geological history, a view which is thought to explain — 

 perhaps in combination with larger relative polar wanderings 

 induced by the summation of small absolute polar wanderings 

 — the occurrence of glacial deposits in tropical regions and of fossil 

 tropical plants and coal beds in arctic regions, and the connections- 

 of widely separated continents postulated by biogeographers (see 

 Dacque p. 56, 85). 



The permanence of the oceans and especially of the great ocean 

 depths has been doubted after the discovery that the abyssal faunas 

 are not of older than Mesozoic origin. This fact has, however, 

 been explained in various ways (see Walther, Soergel, Dacque, 

 Chamberlin) without the assumption of a late origin of the abysmal 

 depths and it has, on the other hand, been pointed out by Penck 

 by means of a simple calculation that the middle depth of the ocean 

 may at all times have amounted to about 2640 meters, since at all 

 times there is evidence of dry land; and that even if one assumes a 

 contribution of 10 per cent to the hydrosphere by juvenile water, 

 there still remains a depth of water of 1800 meters above the 

 middle level of the crust for the beginning of the Paleozoic age. 

 He therefore concludes that the middle depth of the ©ceans was 



