218 Proceedings of the Royal Physical Society. 



ance of the former renders them easily distinguishable by 

 the eye. 



The Kieselschiefer beds are, in almost all the cases I have 

 seen, intensely crumpled and bent into sharply-defined folds, 

 in a way which shows them to have been quite plastic at 

 the time of their contortion. 



(2.) The " Posidonomyenschiefer " are ordinary dark blue 

 or grey argillaceous shales (" blaes " of the Scottish miner), 

 with many impressions of Posidonomya Becheri. Other 

 characteristic forms are Orthoceras striolatum, Goniatites cre- 

 nistria, G. mixolohus. Plant remains are rare in this group. 

 Small beds of limestone occur in these shales at some places. 

 On the south side of the Iberg blocks of a dark lime- 

 stone are found, containing the following Carboniferous 

 fossils : 



Terebratula contraria. Produdus cora. 



Inoceramus carbonarius. Goniatites crenistria. 



Phillipsia alternans. 



There are also patches of quartzite between the Clausthal 

 greywacke and the Devonian limestone of the Iberg, which 

 contain carboniferous limestone fossils, and are regarded 

 by Kayser and others as silicified carboniferous limestone. 

 This limestone appears to have been formed as isolated patches 

 in the neighbourhood of the boundary between the Iberg 

 limestone and the greywacke.^ 



(3.) The greywackes forming the highest division of the 

 Culm are typically developed around Clausthal. They are 

 very rich in felspars, and the sandy, thin bedded varieties, 

 externally resembling fine-grained sandstones, are apparently 

 richer in plagioclase than quartz. Many of the coarse- 

 grained greywackes resemble metamorphic granites, and must 

 be classed as arkose.^ The greywacke of the Harz is a poor 

 building stone, partly because it is difiicultly cut into suit- 

 able blocks, and partly on account of its hygroscopic character. 



It is in these beds that the Culm flora occurs. The plant 



1 Zur Kenntniss des Oberharzer Culm. Jahrbuch der konigl. preuss. geoL, 

 Landesanstalt, 1882, p. 60. 



2 Ibid., p. 65. 



