308 Professor Sedgwick and Mr. Murchison on the 



from them, on both flanks of the chain, by a deposit, remarkable for its 

 character and continuit)', described by us in some detail in a former paper*. 

 This deposit sometimes forms a single terrace, composed of red sandstone and 

 red or variegated gypseous marls, not to be distinguished mineralogically from 

 the new red sandstone series of this country. In other places it contains great 

 subordinate beds of rauchwacke and magnesian limes-tone, and is extended 

 into a succession of undulating ridges, ranging nearly parallel to the escarp- 

 ment of the Alpine limestone. Excellent sections of it, in its more simple form, 

 are seen near Bleiberg in Carinthia, and near the gorge of Werfen on the 

 Salza ; and it is finely exposed, in its more complex form, on the left bank of 

 the Inn, from Hiiring to Schwatz. On the southern flank of the chain it is 

 frequently associated, as is well known, with masses of trap and porphyry ; but 

 on the north flank, igneous rocks are, with very rare exceptions, unknown in 

 this formation. We do not however wish to repeat our former statements, and 

 we only allude to them here for the purpose of introducing- some additional 

 facts observed by one of the authors during his last visit to the eastern Alps. 



(1.) T\\e rauchwacke , OY magnesian limestone, associated with the new red 

 sandstone, is as largely developed near the eastern termination of the Alps as 

 it is in the prolongation of the chain into the Tyrol. Highly instructive sec- 

 tions of this rock were seen at Sobenstein in ascending the valley of the Leytha, 

 previous to a traverse of the primary ridge separating the basins of Lower 

 Styria and Vienna. It is also exposed on the edges of the mountains which 

 close in the south-western corner of the basin of Vienna, whence it runs up 

 into the valleys of St. Johann and Rosenthal, where it is associated with a 

 slaty, red and green sandstone containing casts of certain elongated bivalves 

 resembling Mytilif. Near Kirch-biickl it is traversed by two dykes of ser- 

 pentine, irregular in their directions, but generally bearing- about north and 

 south. 



In its mineral characters and relations^ this porous rauchwacke and yel- 

 lowish magnesian limestone is nearly identical with the rocks in the valley 

 of the Inn, between H'aring and Schwatz ; and like them it forms low ridges 

 and terraces, the beds of which plunge under peaks of Alpine limestone. 



(2.) In the sections illustrative of the general structure of the Austrian 

 Alps;{;, the formation we are describing was made only to appear along- the 



* Phil. Mag. and Annals, N. S. vol. viii. p. 92—96. 



f Similar casts of bivalves occur in the same red sandstone of the Salzburg Alps. The pre- 

 sence of organic remains in this formation is in harmony with the facts discovered in Alsace by 

 M. Voltz and others. 



\ Phil. Mag. and Annals, N. S. vol. viii. pi. 2. 



