8oo 



NA TURE 



[December 16, 1922 



westward drift ; but he viewed the oceanic areas as 

 representing sunken land. This widely accepted 

 notion is rejected by Wegener at the outset. 



We may ask why the skin of a contracting globe 

 became too small for the interior, and split along rifts 

 which ultimately widened into oceans. The answer is 

 that our globe is not contracting. It may even be 

 expanding through rise of temperature, and Joly's con- 

 clusions are quoted as to the influence of radium in the 

 crust. Wegener thinks that Pickering, when, in 1907, he 

 fitted Africa and S. America together in a retrospect, was 

 wrong in assigning an Archsean age to the great rent. 

 The present separation (p. 7) must have occurred since 

 Cretaceous times, if we are to account for the similarity 

 of structural features in the two continents. That is 

 to say, if we reject the notion that the ocean-floors 

 represent subsided land, and if we find similar succes- 

 sions of strata, and ranges with similar orientations, 

 in two separated continental blocks, these blocks must 

 have drifted apart. We should observe the importance 

 of that first " if " ; if we agree with Wegener's hypo- 

 thesis of the inadequacy of vertical movements of the 

 crust, we are in a fair way towards salvation. " Die 

 Theorie der Kontinentalverschiebungen vermeidet alle 

 diese Schwierigkeiten." Even if contraction is going 

 on below, horizontal contraction of the continental 

 surfaces, by " Zusammenschiebung " and consequent 

 crumpling, goes on faster (p. n), and this causes a 

 rending of the sial. To Wegener this does not seem to 

 open up a new series of " Schwierigkeiten." It explains 

 so much that it seems to require little explanation. 

 Yet is not this a return to the conception of a Great 

 First Cause ? Accept that, and all thereafter will run 

 smoothly. 



Here again we may be charged with speaking lightly. 

 Wegener is dealing with possible natural events. Build 

 up an earth on certain lines, endow its parts with certain 

 properties, some of which are suggested by well sub- 

 stantiated experimental work, and certain results are 

 rendered probable. 



The great length of geological time can always be 

 appealed to as a factor. We may now ask what 

 causes continental lands to drift and waltz. We learn 

 (p. 132) that there is a tendency for the blocks to move 

 towards the equator, like other bodies capable of sliding 

 over the main curved surface of an oblate and rotating 

 earth, and that a westward drift may also be expected. 

 The island-loops, the garlands, are detached portions 

 left behind ; oceanic islands, however much they may 

 be disguised by igneous upwellings, however much they 

 may resemble volcanic cones built up from the depths, 

 are similar fragments stranded on the sima, children 

 that could not keep pace with their parents in the 

 movements of the continental dance. 

 NO. 2772, VOL. I 10] 



This is perhaps the boldest stroke of all ; but the 

 suggestion is continued on a larger and more serious 

 scale. New Zealand is bereft of a relative that has 

 hurried forward as Australia, Ceylon is cast off from 

 the foot of India, Madagascar from the African flank. 

 Prof. Wegener reads widely, and he uses biological and 

 geological details that suggest analogies and former 

 continuities. He quotes even (p. 40) Lange Koch's 

 recent tracing of the Caledonian folding into Greenland 

 (see Nature, vol. no, p. 91), though he fails to recog- 

 nise the significance of Sigillaria in S. Africa or of 

 Glossopteris in northern Russia (p. 68). Having 

 rejected the probability of land-bridges and sunken 

 regions, the floor of the Indian Ocean becomes for him 

 a sheet of sima, left bare by separation of the con- 

 tinents, and we need no longer look wistfully for the 

 lost forests of Gondwana Land, as the flying fish come 

 on board to tell us of the secrets of the seas. 



The trough- valleys that have been traced from Suez 

 to the Shire River, though their origin is still under 

 discussion, are regarded as signs of a rift that threatens 

 Africa. In Fig. 36, p. 117, we have the author's view 

 of what may occur under such a trough ; since the 

 walls are separating, room is allowed for a sinking down 

 of fragments from them, while sima is rising under 

 them from below. It is obvious that a melting off of 

 the base of subsiding portions in the sima, such as the 

 author elsewhere contemplates, would allow of a very 

 different representation, and that Wegener's drawing is 

 inspired by his rejection of vertical movements in the 

 sial. Even fjords, despite their barriers of continuous 

 rock, are for him cracks widening by lateral movement 

 as an ice-load presses on the coast. 



Wegener's strong case against general movements 

 of subsidence and evatelion lies of course in his 

 discovery (pp. 19-21) that the great majority of ocean- 

 depths lies near 4700 m. below, and of land-heights near 

 100 m. above, the level of the sea. Attention was 

 directed to this by the reviewer in Nature (vol. 109, 

 p. 202) of the second edition of Wegener's work. The 

 conception of flotation is thus strongly supported ; 

 but it is already part of the doctrine of isostasy. Geo- 

 logical difficulties in Wegener's hypothesis are discussed 

 by Philip Lake in his review of the second edition in 

 the Geological Magazine for August 1922. Literature 

 accumulates on the subject, and we have to consider 

 such general papers as those of Harold Jeffreys " On 

 certain geological effects of the cooling of the earth " 

 (Proc. R. Soc, vol. 100, Sect. A, p. r22, 1921), where 

 account is taken of the fracturing of a primitive crust, 

 and such local studies as those of H. A. Brouwer on 

 the garland-isles of the Dutch East Indies (Journ. 

 Washington Acad. Sci., vol. 12, p. 172, 1922). Brouwer 

 regards the garlands as the crests of growing anticlines, 



