NO. 31 GEOLOGICAL STRUCTURE OF THE ALPS — WILLLS 5 



have been fully described by Professor Rothpletz in the article 

 already referred to. (Seep. 2.) 



Beneath the valley and adjacent hills is a thrust plane which is 

 nearly horizontal. It is exposed near Lenk in the very bottom of the 

 valley, and has long been recognized by Swiss geologists as one of the 

 major structural features of the " zone des Cols " and of the " Nie- 

 sen." We observed that the Flysch at this contact rests upon the 

 nummulitic Eocene ; that is to say, that the terrigenous sandy shales 

 had been thrust upon the marine limestone o£ the same general period. 



The relation of this nearly horizontal thrust plane to those which, 

 at steeper inclinations, traverse the hills on either side is that of a 

 major thrust to minor thrusts of the same system, as shown by B, B 

 to AA', Fig. I. The general dip is northwestward. In that direction 

 the minor thrusts join the major thrust and the system is represented 

 farther northwest by other minor thrusts. 



In a region like the Alps, where thrust planes have been folded, the 

 direction of thrusting cannot safely be inferred from the dip of a 

 single plane. But granting this, it is quite a different matter when the 

 inference rests on the agreement of several minor thrusts and the 

 major thrust from which they spring. The system of major and 

 minor thrusts to be seen at Lenk demonstrates that the Flysch of that 

 region and the fragments of older strata included in it moved from 

 northwest toward southeast. 



This observation is surprising, because it is in such marked con- 

 tradiction to the fact that European geologists have in recent years 

 given up the idea of movements from the north or northwest. They 

 appear to have abandoned the field too readily to those who assert 

 that the Alps have been pressed northwestward only. At Lenk there 

 is clear evidence of southeastward movement. 



It will be necessary to identify this m_ass which has been thrust 

 southward, in its southern extension. But before doing so, it is desir- 

 able to refer here to the great thrust that underlies the Wildstrubel 

 and other portions of the Bernese Hautes-Alpes (CC, Fig. i). It 

 is, of course, well-known. With the superb recumbent fold which is 

 so magnificently exposed in the face of the Wildstriibel, it consti- 

 tutes a most striking example of that structure which is now described 

 as a " pli-nappe," and which Rogers first recognized in the Appa- 

 lachians as an overturned anticline and reversed fault. Heim eluci- 

 dated the mechanics of the structure. It has been experimentally 

 reproduced. The overturned anticline precedes displacement on the 

 thrust plane when a couple of opposed forces develops in strata in 



