306 Professor Sedgwick and Mr. Murchison on the 



the northern side of the chain, the central system seems to pass gradually into 

 the next superior group^ through the intervention of argillaceous and chloritic 

 schist, with subordinate bands of limestone*. 



2. Cry stalUne Rocks icith Calcareous Beds, in some rare instances containing 

 traces of Organic Remains, the sj/stem graduating at its upper extre- 

 mity into Rocks conforming to the ordinary Transition type. 



We pretend not to define the inferior limits of this subdivision, nor do we 

 assert that it can be followed throughout the chain; but it unquestionably 

 exists, as a natural group, in the eastern Alps, as we have proved in our pub- 

 lished paper f. The occurrence of encrinital limestone in association with 

 mica slate and chlorite slate (near the village of Tweng, at the foot of the 

 Tauern Alp), was a new and important fact in the history of this portion of 

 the chain. Similar mineralogical associations, however remarkable at first 

 sight, have been observed in the western Alps ; and encrinital stems do not 

 by themselves define the age of any rock. But we have shown that in this 

 instance the encrinital limestone is not only interlaced with the central system 

 of the chain, but that it is inferior to a long series of strata which every geo- 

 logist has placed below the secondary system of the Alps. In short, this sin- 

 gular group, with the subordinate encrinital limestone, is surmounted by an 

 immense succession of deposits, which gradually present a coarser and more 

 mechanical texture, and at length acquire an undeviating inclination towards 

 the north, by which they are carried under the great precipices of secondary 

 limestone. At the upper limit of these deposits, and therefore on the confines 

 both of the secondary and transition systems of the Alps, occur those great 

 masses of sparry iron ore which are so extensively worked on the northern 

 side of the central axis|. 



At Bleiberg in Carinthia, on the south side of the central axis, we also 

 found transition rocks with organic remains precisely in the place where, 

 theoretically, they might have been expected. In that region the metalliferous 

 dolomites are based upon red sandstone and red gypseous marls ; and the 

 whole secondary system rests unconformably upon coarse greywacke passing 



* See Phil. Mag. and Annals, N.S. vol. viii. August 1830. 



t Phil. Mag. and Annals, N. S. vol. viii. p. 87—91. 



X The sparry iron ore of the Hartz is subordinate to the slate rocks, and is we believe in some 

 instances arranged in irregular masses round the protruding bosses of granite. This position 

 seems to indicate an origin of the sparry iron ore connected with some of the causes which pro- 

 duced the protrusion of the granite. 



