464 ProJ\ Bmkland on the Structure of the Alps, [June, 



bardy, and sink beneath the tertiary formations of the basin of 

 the Po; while the north calcareous belt, being disposed in a kind 

 of trough shape, has a double dip and double escarpment, dip- 

 ping northwards along its line of junction with the central pri- 

 mitive chain, but changing its inclination, and again rising with 

 an highly elevated escarpment also towards the north, along the 

 line of its termination in the Valley of the Danube and of Swit- 

 zerland . 1 



At the foot of this north escarpment, the limestone rests gene- 

 rally on a basis of greywacke, dipping southwards under the 

 limestone towards the central Alps, and being often much dis- 

 torted and even vertical. 



The same greywacke appears irregularly along the base of its 

 south escarpment, and may be seen at Werfen, 50 miles on the 

 south of Saltzburg. 



The south calcareous border rests sometimes immediately on 



Erimitive slate without the intervention of any transition rocks, 

 ut more frequently upon an extensive deposit of red sandstone, 

 red conglomerate, and porphyry, which are considered as belong- 

 ing to the transition formation by Brocchi and most writers on 

 the Alps, but which appear to be contemporaneous with the new- 

 red sandstone formation of England. 



The following order of succession, founded principally on the 

 Tocks that occur in Switzerland and the Tyrol, may be considered 

 as a type of the general structure of the Alps and valleys adja- 

 cent to them. I shall arrange them in classes according to the 

 names by w hich they are generally known on the Continent, and 

 point out the analogies which the component members of each 

 class bear to the strata of England. 



1. Tertiary Formations. 



These formations are principally composed of strata of sand, 

 sandstone, clay, and limestone, of nearly the same age with the 

 formations above the chalk in the basins of London and Paris, 

 and containing subordinately beds of marlstone and coal, in both 

 of which are occasionally found freshwater shells. The sand- 

 stone and conglomerate constitute the molasse and nagelflue of 

 Switzerland, and their order of succession is ; 1. or uppermost, 

 nagelflue ; 2. freshwater formations; 3. molasse. The thickness 

 of 1 and 3 is from 3000 to 4000 feet. The occurrence of fresh- 

 water formations is partial, and their thickness not considerable^ 



The molasse and nagelflue occupy the Great Swiss Valley 

 extending from the Lake of Geneva to that of Constance, from 

 whence they continue down the Valley of the Danube into the 

 plains of Hungary and Transylvania : they are occasionally 

 accompanied by limestone that bears a strong resemblance to 

 the calcaire grossier of Paris. 



II, Younger Alpine Limestone. 



1. Chalk f assuming the form of hard compact limestone^ 



