314 Professor Sedgwick and Mr. Murchison on the 



stone^ but also a thick-bedded, greyish limestone containing Ammonites and 

 numerous specimens of a heart-shaped bivalve. The latter fossil is very pre- 

 valent in the Salzburg- Alps, where it always seems to appear nearly on the 

 same geological parallel ; that is, among rocks corresponding to the lower 

 portion of our oolitic series : but we never procured specimens sufficiently well 

 preserved to have their specific characters determined. 



The Ammonites of the red limestone are of at least five species. None of 

 them can perhaps be strictly identified witli any English species; there is 

 however one, which if not identical with, at least very nearly approaches to, 

 the Ammonites rmdlicostatus of Sowerby- 



It would be entirely foreign to our present purpose to enter on any general 

 details respecting the formation of the lower Alpine limestone, or to point 

 out its enormous expansion in some of the great inner escarpments of the 

 calcareous zones ; nor shall we now describe the modifications of structure 

 by which it passes into vast, crystalline masses, sometimes dolomitic, and loses 

 nearly all traces of stratification, and of all subdivisions similar to those we 

 have attempted to establish. These modifications are now well known, and 

 have been often described by persons possessing iucomparably better means 

 than we had of studying- the mineral structure of the chain. 



5. Shale, Limestone, and Sandstone, with brecciated, saliferous Deposits. 



"We showed in our former paper that some of the great saliferous deposits 

 of the Alps, occupy an intermediate position between the older and younger 

 portions of the calcareous zones. Such is the position of the saliferous 

 masses of Hall, Hallein, and Ischel, given in our published sections*. We 

 now add, in confirmation of our views, a section throug-h the salt works of 

 Halstadtf. 



The salt of Halstadt occurs at a considerable elevation, in a depressed or 

 contorted mass of the Alpine limestone. To reach the works, you ascend 

 from the lake up an almost precipitous face of limestone ; first to a boss, on 

 which is built the ancient tower of the Emperor Rudolph, and afterwards to 

 the height of about 1200 English feet above the lake, where you reach the 

 level of the lowest gallery. There are eight principal galleries by which the 

 salt is extracted, and as the highest is 2343 feet above the lake, the salt mass 

 must be at least 1100 feet in perpendicular thickness. Its total thickness 

 however is not yet ascertained ; because no gallery can be driven at a much 



* Pliil. Mag. and Annals, N.S., vol. viii. pi. 2. figs. 1,2, 5, 6. 

 t Pla(e XXXVI. fig. 10. 



