HYPOGEIC WORK. 



367 



5. Foreign Examples of Tertiary Mountain-making. 



1. The Alps. — Among foreign mountain regions those of the Jura 

 Mountains and the Alps — the two combined in system — have been most 

 carefully studied. The former are much like the Appalachians in ilexures, as 

 first pointed out by H. D. Rogers. The Alps have far greater complexity. 

 The able work of Heim on mountain-making, based on his study of the 

 Toedi-Windgsellen group, gives a full exhibition of the structure in that part 

 of the Alps, and lays down many principles in orography. The section on 

 page 102, showing overturn folds, is reduced from one of Heim's sections. 

 One of the overthrust folds in the region has put the beds upside down 

 over an area of 450 square miles. 50,000 feet of formations of the Jurassic, 

 Cretaceous, Eocene Tertiary and Miocene Tertiary, were upturned at the 

 close of the Miocene period. 



Another remarkable section of overturn flexures in the Alps, worked out 

 by Eenevier, is represented in Fig. 340. The Dent de Morcles stands between 



Rosseline 5479 ft. 



tr.w.Jv^ 



Profile of the Dent de Morcles. Tert. 1, Numraulitic Eocene Tertiary ; Tert. 2, Upper Eocene Tertiary, 

 called the Flysch ; Cret. 1, the Neocomian or Lower Cretaceous; Cret. 2, theUrgonian, a higher division of 

 the Lower Cretaceous. Scale, sjjgos for height and length. Renevier. 



Martigny and Bex on the east side of the Rhone. Cretaceous and Tertiary 

 strata, making the top of the mountain, here lie upside down on Tertiary and 

 older formations. One of the Tertiary formations, the Upper, is folded over 

 on itself. The overturn is indicated in the figure by the lettering. The 

 Cretaceous strata below the plane of the overturn are absent ; but above it 

 there are two strata of the Lower Cretaceous. It is probable that Jurassic 

 beds once made the top, and have been removed by denudation. 



As stated above, the Jura Mountains, northwest of the Alps, are part of 

 the Alps mountain system. The following section (Fig. 341) illustrates the 

 fact that the flexures are overthrust in a northwest direction, like that in 

 the Dent de Morcles, as if the thrust-force came from the southeastward. 

 This direction is not, like that in the case of the Appalachians, from the 

 ocean, but toward it. 



The thickening or the expanding of the beds in the summit of a steep 



