Vol. 63.] ATTRIBUTED TO THE SAVOY AND SWISS ALPS. 295 



The strata in the above-named belt exhibit, as is well known, very 

 remarkable contortions, which have been carefully studied during 

 the last few years by Profs. Bertrand, Termier, Haug, and Lugeon 

 (not to mention others), who, while differing on certain points, are 

 in general agreement with the views expressed by the last-named 

 to the Geological Society of France. 1 He states that the outermost 

 zone of this belt — the Prealpes exterieures, often actually over- 

 lies the Miocene conglomerate and sandstone, and frequently exhibits 

 peculiar flat folds (plis couches), which may be compared to a 

 doubled-up duvet, perhaps together with the counterpane. The 

 strata forming these recumbent folds apparently have no under- 

 ground continuations, and the higher loops commonly extend farther 

 north than the lower. The innermost zone — the Haute s Alpes — 

 consists of generally similar rocks ; but here the contortions are of 

 a more ordinary character, and the beds involved are seen to rise 

 above the surface in the usual manner. Between these two zones 

 is one (Prealpes medianes) with intermediate characters. This 

 unusual folding — these extensive, almost flat layers (nappes) 

 simulating horizontal stratification — Prof. Lugeon explains by sup- 

 posing that the strata thus affected were deposited far away to the 

 south-east ; for instance, in the case of the Chablais district, to the 

 south of the present Pennines, perhaps not far from the region now 

 indicated by a broad belt of greenstone, extending from Locarno to 

 Ivrea. 2 The thrust which drove these sedimentary deposits north- 

 ward was powerful enough to produce overfolding in that direction ; 

 and as it continued the great loops were flattened out, and gradually 

 forced over and beyond the crystalline masses (which were also 

 rising). Thus, after crossing the line of the present Rhone Yalley and 

 the crystalline axis which now culminates in the Finsteraarhorn 

 group, they overrode and, to some extent, became implicated with 

 the contemporaneous strata which still form the lower part of the 

 Chablais Alps, with their Swiss extensions. 



By movements of this kind Prof. Lugeon explains the remarkable 

 contortions and complexities of the zone near the northern margin 

 of the Alps between the courses of the Arve and the Aare, supporting 

 his view by many detailed descriptions and illustrative sections. 

 Convincing as the latter may appear on paper, we must not forget 

 that representations of a highly-disturbed district like the Alps in 

 and to the north-east of the Chablais district must be to some 

 extent hypothetical, because so much rock is either inaccessible or 

 concealed, and that the sections may permit more than one ex- 

 planation. In fact, as Prof. Lugeon frankly admits, they have 

 been differently interpreted by other Swiss geologists. 



It may seem presumptuous for one, whose knowledge of the dis- 

 trict on which Prof. Lugeon chiefly relies is neither minute nor 

 recent, to differ from his conclusions ; but my unbelief relates to 



1 See especially Bull. Soc. geol. France, ser. 3, vol. xxiii (1895) p. 572, & 

 vol. xxiv (1896) p. 535 ; ser. 4, vol. ii (1902) p. 411, & vol. hi (1903) p. 711. 



2 Bull. Soc. geol. France, ser. 4, vol. i (1901) p. 810. 



