244 Proceedings of the Royal Physical Society. . 



over many parts of the Harz. Some of it is distinctly inter- 

 bedded with the Devonian rocks, but it is equally certain 

 that perhaps much more is intrusive, and hence of later date 

 than the strata immediately surrounding it. There can, how- 

 ever, be little doubt that it is all older than the granite, and 

 has either been poured out over the surface or injected into 

 the underlying beds at some part of the Devonian or Lower 

 Carboniferous period. 



A. Interhedded Diabases. — Diabase of unmistakable sub- 

 aerial origin occurs at two places on the Harz interstratified 

 with Middle Devonian " Stringocephalus beds." (1.) It 

 stretches in a long narrow band (" Diabaszug ") from Osterode 

 north-eastwards to Altenau, where it thins out and seems to 

 disappear. It is here highly inclined, and, dipping to the 

 south-east, rests on a thin band of Goslar shales, against which 

 the Culm greywacke appears to have been brought down by 

 a fault. (2.) The other interbedded diabase occupies a well 

 defined area in the Elbingerode basin, about. 13 kilos in 

 length from east to west, and 5 kilos in breadth. Both 

 volcanic rocks are associated with beds of tuff (Schalstein) 

 and workable hsematite, and are slaggy and amygdaloidal on 

 their upper surfaces. The strata below these diabases are 

 but slightly, if at all, altered, and there appears to be no sign 

 of metamorphism in the fossiliferous shales and tuff beds 

 between the different sheets. 



B. Intrusive Diabases. — The other diabases are divided by 

 Lossen into two classes — (1.) Diabase in the Hercynian and 

 Lower Devonian formations, and (2.) that in the Goslar shales 

 and Culm. 



(1.) The diabase in the Hercynian beds of the Lower Harz 

 occurs in a great multitude of patches of different size. The 

 largest of these is at St Andreasberg, where it reaches a length 

 of about 6J kilos. The patches are generally, however, of 

 small size, and occur in groups at particular places, e.g., in 

 the district to the north and east of Harzgerode, around 

 Treseburg on the Bodethal, and in the district south of 

 Wernigerode. At all these localities it is marked on the 

 map as lying within the area of the Wiederschiefer, and 

 indeed it is found so often in or near the same position that 



