NO. 31 GEOLOGICAL STRUCTURE OF THE ALPS — WILLIS 3 



(3) The isolated masses of pre-Eocene strata, which have been 

 called remnants of the tete or front of the same pli-nappe, and others 

 which I saw near Chateau d'Eux, have been cut off by intersecting 

 overthrusts. They first moved southward or southeastward and later 

 northward or northwestward, in both movements rising on the inclined 

 thrust planes. Their present position is thus above but not distant 

 from that which they originally occupied. The same is true of the 

 so-called " exotic " masses of the Prealpes which constitute the 

 " tetes " of the hypothetical nappes des Klippes. 



(4) The thrust which divides the pli de Morcles from that of the 

 Diablerets is a minor thrust plane rising from a major thrust plane 

 that underlies the Ilautes-Alpes, and is one of asystemof minorthrusts 

 which, with the major thrust, constitute a single complex structure of 

 the Scottish Highland type. 



(5) Since the principal concrete example of a " pli-nappe " or 

 nappe de recouvrement, that of the Wildhorn-Wildstriibei, is, accord- 

 ing to my observation, not a pli-nappe but an effect of two intersecting 

 thrusts, I am unable to accept the reconstruction of less complete 

 nappes de recouvrement, which, according to modern theory, were 

 once piled up, one overriding the other, to form the Alps. I regard it as 

 probable that the recognition of intersecting overthrusts and of sys- 

 tems of major and minor thrusts of the Scottish type, combined with 

 unusual but incidental folding, will eventually be found to explain a 

 large part of Alpine structures. 



The observations which led me to these views were as follows : 

 First, as to the existence of thrusts from opposed directions. The 

 evidence of that fact I first observed near Lenk, in the valley and 

 heights, up to and including the base of the Wildstriibel. It is 

 stratigraphic, structural, and physiographic. For identification of 

 strata in the field on paleontologic evidence I am indebted to Professor 

 Rothpletz, whom I chanced to meet at Zweisimmen and with whom 

 I examined the locality. We there discussed and verified our obser- 

 vations of structure. The physiographic relations, which had great 

 weight with me because I had seen similar effects in the Lewis Range 

 of Montana, were unfamiliar to him as a basis of inference, and may 

 be regarded as an independent line of reasoning. 



The stratigraphy of the district of Lenk, which lies in the southern 

 Prealpes, is well established. The Triassic, Jurassic, and Eocene are 

 more or less fully represented by very distinctive formations which, 

 in the order named, are essentially gypsiferous shales or gypsum 

 (Triassic), blue marine limestone (Jurassic), and sandy brown shales 



