4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



(the fades of the Eocene, commonly called "Flysch"). The Cre- 

 taceous is scarcely present, there being a marked hiatus between the 

 Jurassic limestones and the earthy red lime-shales that correspond to 

 its hig-hest horizon. The Flysch, which was originally a very thick 

 formation, has been thickened by folding and thrusting, so that it 

 constitutes the dominant rock of the hills. The Jurassic limestone 

 and the Triassic gypsiferous shales occur in the Flysch as fragments 

 which have been separated from their original connections by thrust- 

 ing. 



The internal structure of the Flysch is obscured by sward, but its 

 principal features may be traced by the fragments of pre-Eocene for- 

 mations. Where Jurassic or Triassic rests upon Flysch, the contact 

 of the older upon the younger formation is obviously a thrust plane. 

 Where two or more such contacts, though somewhat apart, fall into 

 a common plane of dip, they may reasonably be connected as belong- 



Vrealjoes ^, Hatxtes Alpes 



^-' ^„-^ ^WudstrubeL ,„ 



D"' 



C 



Fig. I. — Diagram of intersecting thrusts observed near Lenk and in the 

 Wildstriibel. 



A A' A" A'" := plane of a major thrust from the northwest. B, B,B, = mmor 

 thrusts branching from the major thrust AA' and belonging to one system with 

 it. CC' = thrust from the southeast, intersecting and disturbing the older 

 thrust AA'A"A"'. DD' and i}"i5"' = surface of erosion developed after the 

 thrust AA'A"A"' and before the thrust CC ; dislocated by the latter and 

 involved in the elevation of the Hautes-Alpes. 



ing to one and the same thrust. And where several such planes lie 

 parallel one to another, they form a system of thrusts ; such, for 

 instance, as that diagrammatically represented by the minor thrusts 

 B, B, B in Fig. i. 



Near Lenk, in the hills which rise on each side of the valley that 

 is eroded across the strike, this structure is clearly represented by the 

 fragments of Jurassic limestone that form little scarps in the smooth 

 grass-grown slopes of Flysch. Having traced out the several parallel 

 thrusts on one side of the valley, one may identify each one on the other 

 side by corresponding features of the hills and slopes. This Professor 

 Rothpletz and I did, and we observed that the planes of these parallel 

 thrusts dip northwestward at moderate angles. Our observations 



