August 22, 1907] 



NA TURE 



42: 



THE MAKING OF MOUNTAINS. 

 'TPHE profound impression made on contemporary geo- 

 logical thought by what is known as the Schardt- 

 Lugeon theory ot overfolding is well seen in Herr H. 

 Hoek's last paper on " Das zentrale Plessurgebirge " 

 {Bcrichte d. Naturforsch. Gesell. zu Freiburg i. B., Bd. 

 xvi., 1906, p. 367). In this he completely modifies his 

 reading of the district, published three years ago, in favour 

 of one that brings it into structural harmony with recent 

 views as to the existence of " Ueberschiebungsdecken," 

 '* Nappes de recouvrement," or overlapping and over- 

 thrust recumbent folds. The region south-east of Chur has 

 received a good deal of geological -attention, and Herr 

 Hciek claims that it now falls into its place as a structural 

 link between the overfolded areas of Switzerland and the 

 Austrian Alps. His paper is written in a considerately 

 argumentative spirit that provides cheerful reading, and 

 concludes with a tilt at Rothpletz, who has sprung into 

 the same field of inquiry. Both writers agree, however, 

 that the overlying rock-sheets of the Plessurgebirge have 

 been brought into the area from a distance ; and that is 

 the point which interests the watchers of the tourney. 



Dr. W. Hammer, in a review of the above paper 

 {]'erhandl. d. k.k. gcol. Kcichsanstalt, 1906, p. 383), 

 evidently regards it as an attempt to put an old wine 

 of good quality into new and uncertain bottles. But Herr 

 G. Steinmann adopts Hock's typical landscape of the four 

 overthrust sheets above Parpan in his " Geologische 

 Probleme des Alpengebirgs " (p. 40), and he has had 

 ample opportunity of discussing the structure with the 

 author. Steinmann 's paper, published by the Dcutschcr 

 und bsterreichischer Alpenverein at Innsbruck in 1906 

 (Bd. 37 of their Zeitschrift), is a delightful exposition of 

 the older and later views, beginning with the Juras and 

 ending in the east of Switzerland, and is written for the 

 ordinary traveller as well as for the geologist. The land- 

 scapes, in which the beds are duly labelled, are accom- 

 panied by an admirable series of sections, often showing 

 the two rival readings, and gathered from various .authors. 

 Steinmann 's own sections show clearly the stages of 

 growth which are held to have culminated in the system 

 of overfolds in Switzerland. This lucid paper seems to us 

 perfect for its purpose, and the author is able, in his 

 separately issued copies, to reproduce Dr. von Seidlitz's 

 panorama from the Kunihorn, which was published in part 

 only in the Zcitschrijt dcs Alpcnvereins. 



fierr Schardt himself ha? furnished, in the Verhandl- 

 ungen der Schweizcrischcn Naturforscheuden GcscUschaff, 

 St. Gallen meeting, 1906, p. 308, a welcome account of 

 " die modernen Anschauungen fiber den Bau und die 

 Enstehung des .'\lpengebirges. " Already this distinguished 

 author suffers from an extremist group of followers, and 

 he humorously characterises some of Termier's work as 

 an exhibition of " Ultranappismus. " The coloured 

 sections illustrating Schardt 's paper supplement this very 

 clear exposition of his views. On p. 343 ho emphasises 

 the importance of gravitational sliding in producing certain 

 features of steeply elevated and compressed folds, and 

 points out that this influence has been too often under- 

 estimated. 



Travellers in the most familiar part of Europe will akso 

 profit greatly by Herr A. Baltzer's " Das Berneroberland 

 und Nachbargebiete " (Berlin : Gebriider Borntraeger, 1906, 

 pp. xv-f 347). The price of this handy book, 12.50 marks, 

 includes a general volume, which has not yet reached us, 

 though it was announced to appear during last winter. 

 Rothpletz 's work on the overfolded area of the Rhactic 

 .Alps, to which Hoek refers in the paper above noticed, has 

 been published in the same " Sammlung geologischer 

 Fiihrer. " Baltzer's volume starts in the Bernese Juras, 

 among the romantic clnscs, guides the pedestrian of geo- 

 logical tastes to the typical sections around Grindelwald, 

 and brings him back by the St. Gothard railway and 

 Lucerne. The illustrations are not always so neat as those 

 of Steinmann, but cover a great amount of detail. The 

 transparent sheets on which the names of the rock-layers 

 are printed, which are used as indexes to several of the 

 photographs, strike us as a little awkward in a book that 

 must be used in all weathers in the field. Among the 

 many useful diagrams is one (Fig. 69) showing the folded 



NO. 1973, ■^'OL. 76] 



strata as viewed from the steamer on both sides of the 

 lake of Uri. 



Dr. C. Sandberg (Transactions of the Geological Society 

 of South Africa, vol. ix., Johannesburg, 1906, p. 82) gives 

 a new reading of the folded structure underlying " the 

 innocent looking, softly undulating Karroo Formation " in 

 the Prince Albert district of Cape Colony. The country, 

 with its bare kopjes and its abundance of rock-exposures, 

 lends itself to stratigraphical investigation. The Tvgerberg 

 shows on its south side the Witteberg series resting on 

 the Dwyka conglomerate, which properly overlies it, while 

 the Dwyka series occurs again on the north side of thr> 

 hill. This can be explained by fan-structure, the Witteberg 

 series coming up along a local anticline, which has ex- 

 panded southward as an overfold. Though various authors 

 show various dips, the anticlinal view has been generally 

 accepted. Dr. Sandberg, however, quoting the magic 

 names of Schardt, Lugeon, and Termicr, reads the struc- 

 ture as the downward-turned, or, shall we say, pseudo- 

 synclinal, end of an ovcrpushed anticline, the root of which 

 lies away in the Zwartebergen to the south. Mr. A. W. 

 Rogers, who is invoked by the writer, points out that a 

 section quoted from him in support does not touch the 

 Tygerberg, and he evidently prefers the older view for the 

 present (Proceedings to accompany the above volume, 1907, 

 p. liii.). But Dr. Sandberg's paper serves as a fresh 

 indication of the keenness and vitality that prevail in South 

 -African geology. 



It is evident that very few geologists now doubt that 

 overfolds occur in the earth's crust, whereby strata are 

 moved from their place of deposition over distances amount- 

 ing to even 100 kilometres. If we grant ten miles for 

 such movements in the north of Scotland, we do not find 

 it unreasonable to allow seventy miles of overthrusting in 

 the more crumpled region of the Alps (see Sir A. Geikie's 

 remarks. Abstracts of the Proceedings of the Geol. See. 

 of London, April 10, p. 67). But the admission raises 

 serious questions as to what happens in the foundations 

 underlying these compressed areas of the crust. Dr. 

 Anipferer, in a lengthy and closely reasoned paper on 

 " Das Bewegungsbild von Faltengebirgen " {Jahrb. der 

 k.k. geol. Reichsanstalt, Bd. Ivi., 1906, pp. 539-622), 

 rejects the theory that localised crumpling is due to 

 the approach of great earth-blocks in the contracting crust. 

 He urges, moreover, that there is nothing in any complex 

 group of rocks, such as we ordinarily find folded together 

 in a mountain-chain, to account for the folding in that 

 particular locality. The local structure determines the 

 details of the architecture (p. 607), but the position of the 

 chain on the earth must be referred to the nature of the 

 plastic foundation, the " Untergrund." The composition 

 of the earth's interior is by no means uniform (pp. 608 and 

 609), and both physical and chemical changes in it may 

 produce considerable alterations of volume in one portion 

 or another. These alterations are manifested at the 

 surface, in the sensitive skin of the earth, as local sub- 

 sidences or elevations. The vertical movements of the 

 foundation lead to gravitational sliding, which affects the 

 overlying skin (p. 601), and it is suggested that the folded 

 mountain-chains are formed along lines of more or less 

 intense vertical upheaval, from which the fundamental 

 masses then flow away sidewa^'s, producing the overfolds 

 and crumplings that we perceive upon the surface. The 

 underflow, the " Unterstromung, " is thus Ampferer's main 

 cause of surface-folding, and changes in the living and 

 mobile " Untergrund " determine where " Unterstromung " 

 shall occur. 



We trust that in these few words we have correctly 

 represented Dr. .i^mpferer ; for the paper is not an easy 

 one, and the absence of references to the details shown in 

 many of the diagrams renders these of little help as illus- 

 trations, rig. 41, however, on p. 611, shows suggestively 

 how the irregularities of the foundation or " Untergrund " 

 may be ascertained by a comparison of the geological 

 history of areas on the earth's surface. .Areas with similar 

 foundations may be expected to subside together or to be 

 elevated together during geological time. It is easier to 

 estimate the amount of subsidence that took place during 

 any epoch than the amount of elevation, the latter being 

 marked by no characteristic sediments ; but we may hope 

 eventually to represent the history of an area by a curve 



