6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



the zone of moderate load and folding; but when dislocation origi- 

 nates in the deeper zone, where excessive load prevents competent 

 folding, the movement, on being transmitted to strata in the zone of 

 folding, may produce a recumbent anticline as an incidental structure. 

 Displacements of the former class are usually of moderate horizon- 

 tal throw, rarely more than ten or twenty kilometers, but they may be 

 features of a very extensive general movement. Such I take this 

 pli-nappe of the Wildstriibel to be: an overturned anticline which 

 has been pushed far enough to dislocate the middle limb, although 

 not necessarily to a great distance. It is, however, a striking feature 

 of the pronounced movement of the mass of the Alps from southeast 

 toward northwest. Since there is no question of this movement 

 toward the northwest, we may accept it without discussion. 



I must here advert to the difference of facies between the strata 

 of the Prealpes and those of the Hautes-Alpes. The former is an 

 incomplete sequence, comprising but a few of the Mesozoic stages 

 and the Eocene. The latter is a very complete succession from Trias- 

 sic to Eocene inclusive. The one is composed chiefly of sands and 

 muds, the other of marine limestones. The contrast could scarcely 

 be more marked. 



Accepting this well-known distinction, we may say that the two 

 facies are superimposed, each on the other, by the thrusts from oppo- 

 site directions. The Flysch of the Prealpes, in being thrust toward 

 the southeast on the major thrust plane, came to rest on the surface 

 of the marine nummulitic Eocene of the facies of the Hautes-Alpes. 

 This contact is seen in the valley floor near Lenk, as already de- 

 scribed. The marine strata which form the Hautes-Alpes may, in 

 turn, be seen superimposed on the Flysch at the base of the great 

 cliffs which form the face of the Wildstriibel south of Lenk, The 

 contact marks the thrust plane, which dips southeast and on which 

 movement was toward the northwest. 



Having become convinced, contrary to my expectations, but by my 

 own observations, that the structures of this district comprise two 

 intersecting systems of overthrusts, I sought to determine which 

 might be the older system. The evidence on this point is unequiv- 

 ocal. 



Going from Lenk southward to the base of the Wildstriibel one 

 may observe that the major and minor thrusts of the system on which 

 displacement was southward rise in the hills. Near Lenk the planes 

 dip nearly uniformly. Near the base of the Wildstriibel they are 

 folded into anticlinal and synclinal structures. Although long fa- 



