9.4 Prof. Sedgwick and Mr. Murchison on the 



abutting against the preceding group ; also in its prolongation 

 abutting against highly inclined beds of grauwacke slate. 



(5.) A series of highly inclined beds of grauwacke slate, 

 succeeded or cut off' by an irregular mass of trap. 



(6.) Trap, which traverses the ravine and occupies the 

 banks of the rivulet for several hundred feet. It is close- 

 grained, of a dark greenish colour, and breaks into irregular 

 fragments at a number of earthy ferruginous joints. We have 

 no specimens of this rock; but it may we think be regarded 

 as a variety of the black porphyry, or melaphyre of De 

 Buch. It contains several fragments of white crystalline 

 limestone, and here and there passes into a conglomerate with 

 a cement of iron clay. 



(7.) The trap is immediately succeeded by grauwacke slate, 

 with the subordinate thin beds of limestone above described, 

 containing Encrinites, Spirifers, Productae, &c. Further down 

 the valley, and at the south base of the Schlossberg, the red 

 sandstone series is seen for several miles overlying the grau- 

 wacke series and underlying the Alpine limestone. 



The great faults, which have not only brought out the red 

 marl and sandstone, but have made the dolomite of the 

 Erzberg to abut against the grauwacke of the Windisherberg* 

 — the singular contortions and breaks of the formations — the 

 appearance of the trap and trappean conglomerates, not merely 

 the accompaniments but probably the causes of the disrup- 

 tions — the unusual occurrence of organic remains decidedly 

 of the transition class — the clear relations (notwithstanding 

 the local confusion) of the transition and secondary systems 

 — all these circumstances together make the sections in the 

 neighbourhood of Bleibero- the most instructive we have seen 

 in the Alps. 



On the south side of the chain, porphyry is said to be in 

 many instances subordinate to the red sandstone. In the val- 

 ley above Ponteba we found red sandstone passing into con- 

 glomerate with pebbles of porphyry; and in the range of the 

 formation, towards the west, porphyry becomes so extremely 

 abundant as to predominate over, and in some instances 

 almost to take the place of, the red sandstonef. 



It 



* Plate II. fig. 1. 



■j- The range and extent of this porphyry is well marked in M. Ployer's 

 Map of the Tyrol. One of the sections which best exhibits its relations 

 and intimate connection with the gypseous red sandstone, was well seen 

 between Neumarkt and Cavalese, in a traverse, from the valley of the 

 Adige to Predazzo and the Val di Fassa, made by one of the Authors of this 

 paper in 1828. (PI. II. fig. 7.) The lowest beds observable in ascending from 

 Egna or Neumarkt, on the Adige, to the pass of St. Lugano leading to the 

 Val d'Avisio, and thence to Predazzo, consist of red sandstone with greenish 



marls 



