194 



NA TURE 



[June 29, 1905 



dependent upon the course of mountain chains, are 

 embayed where the sea has flowed over foundered 

 blocks. The vertical relief of the continents is 

 determined mainly by subsidences, by the resistance 

 of great blocks of strata which remain as plateaus 

 high above the general level of the country, and by 

 the crumpling of bands into mountain chains. The 

 course of such crumpled bands is very sinuous, because 

 they have to adapt themselves to the passive resistance 

 of stronger blocks of the crust ; they curve round the 

 margins of the resistant masses, on to the edges of 

 which they may be overthrust. Suess follows, for 

 example, the course of the great .Alpine mountain 

 system from its western end in southern .Spain, 

 through the Atlas Mountains of .Africa, along the 

 the .Apennines through Italy, across central Europe 

 as the Alps and Carpathians, and then through the 

 groat curve around western Roumania and Servia 

 into the Balkans. Its continuity eastward has been 

 broken by the recent foundering of the Black Sea ; 

 but the .Alpine system is continued through the Crimea 

 and the Caucasus, and after another gap, caused bv 

 the subsidence that formed the southern basin of the 

 Caspian, it is continued across Asia through the 

 Himalaya and the chains of Burma into the islands 

 of Malaysia. Suess explains the sinuous course of 

 this folded band by tracing its dependence upon the 

 unfolded blocks, against vihich it has been pressed. 



The theory of the permanence of oceans and con- 

 tinents inevitably receives slight consideration from 

 Prof. Suess. He does not trouble us with the a priori 

 arguments on this question. He simply tells us the 

 contemporary evidence as to the actual age of the 

 continents. Thus he points out that in the Cretaceous 

 period North .America was not ; but it had come into 

 existence at the beginning of the Laramie period, and 

 has lasted ever since. .Similarly the Indian peninsula 

 and .Africa south of the .Atlas are remnants of the 

 Mesozoic plateau-continent of Gondwanaland, which 

 has been severed into two by the foundering of the 

 Indian Ocean in late Cainozoic times. 



Consideration of Prof. Suess 's work inevitably 

 suggests a comparison with that of Lyell. Suessism 

 is sometimes regarded as a rival school to Lyellism. 

 But Suess's essential doctrines are a development of 

 Lyell's views rather than being in direct opposition 

 to them. Lyell, for instance, attacked the belief that 

 volcanoes are craters of elevation ; but, in the 

 necessary darkness of the days before Sorby's in- 

 genuity had rendered microscopic petrology possible, 

 he retained his belief in an axis of elevation for the 

 mountain chains. Suess has now taught us that the 

 axes of elevation of mountain chains must follow von 

 Buch's craters of elevation of volcanoes. Even in re- 

 gard to what is sometimes considered as Prof. Suess's 

 arch heresy — his acceptance of great variations in the 

 ocean level — he is opposed to ultra-Lyellists and not 

 to Lyell. The following passage from the " Prin- 

 ciples " shows that, with Lyell, Ordnance Datum was 

 not a fetish : — 



"This opinion is, however, untenable; for the sink- 

 ing down of the bed of the ocean is one of the means 

 by which the gradual submersion of the land is pre- 

 vented. The depth of the sea cannot be increased at 



NO. 1 86 1, VOL. 72] 



any one point without a universal fall of the waters, 

 nor can any partial depositions of sediment occur 

 without the displacement of a quantity of water of 

 equal volume, which will raise the sea, though in an 

 imperceptible degree even to the antipodes. The 

 preservation, therefore, of the dry land may sometimes 

 be effected by the subsidence of part of the earth's 

 crust (that part, namely, which is covered by the 

 ocean), and in like manner an upheaving movement 

 must often tend to destroy land ; for if it renders the 

 bed of the sea more shallow, it will displace a certain 

 quantity of the water, and thus tend to submerge low 

 tracts." 



One chief diflerence between Suess and Lyell is that 

 Lyell was naturally inclined to exaggerate the import- 

 ance of local earth movements. Prof. Suess, with the 

 benefit of a much wider knowledge than was possible 

 to Lyell, and equal intellectual insight, realises that 

 the geological systems are defined, not by independent 

 local movements, but by changes that are world-wide 

 in scope. Suess's views are not essentially opposed 

 to the uniformity, which Lyell established, in opposi- 

 tion to the preceding belief in catastrophes of 

 extraneous origin. Suess and Lyell both teach us that 

 geological changes are due to cau.ses that are still in 

 action. Geographical evolution, like organic evolu- 

 tion, has not been interrupted by external influences 

 or unnatural catastrophes ; but it does not necessarily 

 follow that the rate of progress has been uniform. 

 There have been periods of geographical revolution 

 due to a rush of movements, that relieved stresses pro- 

 duced by long periods of slow change. Such dis- 

 turbances affect the whole world ; and it appears 

 probable that the correlation of strata in distant 

 regions will depend on palaeontology only for general 

 homotaxis, and on the events of physical geology for 

 the determination of exact synchronism. 



.A second difference between Lyell and Suess is that 

 the former attached a, perhaps, exaggerated belief to 

 the importance of denudation in modelling the surface 

 of the globe. His own studies lay in lands wherein 

 denudation has been more powerful than recent earth 

 movements. The sub-title of his " Principles " — 

 " the Modern CTianges of the Earth and its In- 

 habitants Considered as Illustrative of Geology " — 

 shows his point of view. He taught men that the 

 common geographical features of Europe and Eastern 

 -America were due to the long-continued operation of 

 slow and still active forces ; but he did not fully realise 

 that, elsewhere, the major geographical features are 

 the direct expression of recent disturbances of the 

 crust. 



As to the cause of the distribution of these dis- 

 turbances Prof. Suess has not yet given us his full 

 explanation, and in this volume he rightly held such 

 questions premature. But it is now possible, mainly 

 thanks to his work, to trace one controlling factor in 

 the existing plan of the earth — the alternation of 

 periods of spheroidal recovery due to the earth's rota- 

 tion, with periods of deformation due to the shrink- 

 ing of the earth's internal mass. This factor promises 

 the clue to the periodicity of geological events, to the 

 general world-wide correspondence in the geological 

 formations, and to the distribution of the folded bands 

 and foundered blocks of the earth's crust. 



J. W. G. 



