NO. 31 



GEOLOGICAL STRUCTURE OF THE ALPS — WILLIS 



II 



Thus I regard the Hautes-Alpes of the Bernese chain as consist- 

 ing structurally of a great overthrust mass whose general movement 

 was north by west or northwest on a major thrust plane. There 

 developed simultaneously a number of minor thrusts on which move- 

 ment was toward the west, at an angle to the general motion of the 

 mass. It is an example of major and minor thrusting, with two some- 

 what divergent directions of displacement and with diversities of fold- 

 ing in the several segments. 



It was at the suggestion of Prof. Lugeon that Dr. Jaccard courte- 

 ously conducted me to the vicinity of Chateau d'Eux, where he showed 

 me a typical example of the " tete plongeante " of a nappe de recouvre- 

 ment in the Rhetic limestone of the Pte. de Cananeen. The annexed 

 diagram is taken from Dr. Jaccard's paper.' 



Rocher Plat 

 ^ C.^ /^ SE 



Co,nanee)% 



Fig. 2.— Prealpes near Chateau d'Eux. Characteristic "tete plongeante ^| 

 of a supposed " pli-nappe " represented by the " Breche de Chablais-Hornfluh " 

 (Rhetir) infolded in Cretaceous and Eocene. Otherwise interpreted as a 

 mass overthrust from the left {NW) on the plane AA'A"A'", which now 

 appears folded back by the later thrust CC from the southeast. (Adapted 

 from sketch by Jaccard, pi. 34-' J 



The limestone (" Breche de Chablais-Hornfluh ") is of Rhetic age, 

 according to Jaccard, and the fragment that forms the Pte. de Cana- 

 neen is an isolated synclinal mass, resting upon and enveloped m 

 Upper Cretaceous strata, which in turn overlie the Eocene Flysch. 

 In this inverted order and synclinal structure we may certamly see 

 the plunging head of a great overthrust sheet that has come over all 

 the Alps from the far southeast and buried itself in the Flysch-if 

 such a head and such a sheet have, or possibly could have, any actual 

 existence. I could not. however, accept that concept. I saw, mstead, 



^Jaccard. Frederic: La Region Rubli-Gummfluh ; Bull, de la Societe 

 Vaudoise des Sciences Naturelies, Vol. 43, IQO?, pl- 34- 



