286 



Professor Sedgwick and Mr. Murchison on the 



Netzberg. 



doubt that it is a true eruptive rock : for in the upper part of the Ocker Thai, masses of grauvvacke with 

 organic remains are caught up in it*; and in ascending the Brocken we found several blocks of granite 

 with imbedded splinters of grauwacke. Again, the slates nearly in contact with it, are often converted into 

 hornstone, and the arenaceous grauwacke into quartz rock ; and the junction specimens exhibit almost all 

 those modifications of structure which are so well known in Devonshire and Cornwall. The granite of 

 the Hartz, like that of Devonshire, has however produced but a very small eifect on the general strike of 

 the chain. Yet does it appear to have produced enormous derangements in the position of the subordinate 

 masses : for all the older rocks, extending for many miles on the north side of the granite of the Brocken, 

 are in a reversed position ; and few of the masses near it show any conformity to its surface. — See 

 Section 17. PI. XXIIl. 



Fig. 14. 



w.s.w. 



Inverted and fragmentary condition of the strata north of the Brocken, near Goslar. 



Flank of the Brocken. Rammelsberg. Goslar (N, of). 





E.N.E. 



b b> 



7. Devonian. 



8. Silurian grauwacke. 



a. Greenstones, &c., with Devonian slates. 



b. Granite of the Brocken. 



b'. altered grauwacke on the flanks of the Brocken. 



3. Quartziferous porphyry ( Quarzfiihrender Porphyr). — It rises up in several bosses of considerable 

 extent, in which respect it is unlike the elvans of Cornwall. Yet does it occasionally send out dykes into 

 the neighbouring strata ; and in mineral structure it has close analogies with the commonest varie- 

 ties of Cornish elvan. The specimens of this rock, which we saw near Stolberg, contained a great deal 

 of pinite. These trappean masses are considered, we believe correctly, as newer than the granite, in 

 which respect they present another analogy with the Cornish elvans. 



-t. Newer trappean rocks, overlying and alternating with coal shale, red sandstone (rothliegendes), — 

 These are described in the German maps of the Hartz under the general name of Quarzfreier Porphyr. 

 They are of very varied structure, passing through every shade, from red felspar rock to black augitic trap 

 and basalt. The accompanying woodcut will explain their general relations, both to the newer and older 

 stratified masses, as seen in some remarkable sections near Ilefeld, on the south side of the chain, where 



Fig. 15. 



Hills E. of Poppenberg. Ilefeld. Sachswerfen. 



Kordh 



these porphyries are magnificently developed. Considered as a whole they are undoubtedly true erup- 

 tive rocks ; yet are they most intimately associated with the red sandstone and the thin carboniferous 



* M. Zincken showed us some specimens of granite in which had been caught up fragments of cal- 

 careous rocks with organic remains ; but we do not remember from what part of the Hartz he had ob- 

 tained them. 



