294 PEOP. T. G. BONNET ON THE SOUTHERN ORIGIN [Aug. T907, 



16. On the Southern Origin attributed to the Northern Zone in 

 the Savoy and Swiss Alps. By Prof. T. G. Bonnet, Sc.D., 

 LL.D., F.R.S., F.G.S. (Bead March 27th, 1907.) 



In two most valuable and interesting papers contributed to our 

 Journal, 1 Prof. Sollas has described the results of experiments made 

 with cobbler's wax, and designed to illustrate the internal movement 

 of a viscous fluid or very plastic solid under the action of gravitation, 

 which was set up originally by the wedge-like form of the mass and 

 continued by adding new layers, more or less similarly shaped, of 

 the same material. Complications were introduced, as described in 

 the second paper, by attaching to the floor of the trough used for 

 the experiment, first one, then two, mound-like obstacles over which 

 material, once near its head, was forced by the pressure of that sub- 

 sequently added : the result being the formation in the older layers 

 of some remarkable folds, and even dislocations, especially in front 

 of the second obstacle. 



These experiments, as Prof. Sollas pointed out in his first paper, 

 throw much light on the movements of glaciers 2 ; but whether 

 they give any real support, as is suggested in the second paper, to 

 Prof. Lugeon's explanation 3 of the flexures in the Chablais district 

 and its continuation across the Rhone, is, in my opinion, very 

 doubtful. This hypothesis may be briefly stated in the following 

 terms: — On the northern side of the great crystalline massif, 

 the crest of which forms the watershed of the Pennine-Lepontine 

 Alps, is a second one — that of the Bernese Oberland. Its eastern 

 end, before reaching the Bhine, disappears beneath a thick covering 

 of Secondary and early Tertiary rocks. Its western end also sinks 

 down, but to a less extent, and, after being crossed by the Rhone, 

 presently becomes exceptionally prominent in the parallel folds of 

 the Breven and Mont Blanc, from which it may be traced southward 

 into Dauphine. In front of this northern range of crystalline rocks 

 is a broad belt of sedimentaries — calcareous and argillaceous — which, 

 like those already mentioned, begins generally with the Trias (though 

 this is sometimes wanting) and continues to the end of the Eocene, 

 or even into the Oligocene. Yet farther north are the foothills, 

 formed of Miocene conglomerates and sandstones — the former of 

 which rise in the Rigi to about 5900 feet, and in the Speer to about 

 500 feet higher. 



1 Vol. li (1895) p. 361, & vol. lxii (1906) p. 716. 



2 Incidentally, also, they indicate that Principal Forbes was more nearly 

 right in comparing glacier-ice to a viscous fluid than Prof. Tyndall, with his 

 hypothesis of fracture and regelation in a rather brittle solid. I think it very 

 probable also (but have not yet had time to work out my general idea in any 

 detail) that these experiments will throw much light on the subterranean 

 movements of molten rock, especially when not very liquid, on certain in- 

 clusions of one kind of such rock in another, and on some difficulties in 

 regard to the distribution of volcanoes. 



3 Bull. Soc. geol. France, ser. 4, vol. i (1901) p. 723. 



