216 Proceedings of the Royal Physical Society. 



its sides, to a depth of about 1300 feet (400 m.) below the 

 summit — a fact which appears to point to its having formed 

 a massive resisting body, while the more pliable sedimen- 

 tary strata around it were bent about during the great earth 

 movements which took place in the middle of the Carbonifer- 

 ous period.^ 



This great Devonian coral reef contains, besides many 

 corals (as Ascervularia, Cyathojphyllum, etc.), other fossils in 

 great numbers, e.g. : 



Terebratula elongata. Bhynchonella cuboides, E. Fugnus. 



Spirifer simplex, deflexus, hifidus. Orthis striatula. 



Goniatites Wurmii. Conocardium trapezoidale. 



G. intumescens. Spirigera concentrica. 



Also many species of Natica, Turbo, Pleurotomaria, Loxomena, etc, 



Dr von Groddeck, in his paper just alluded to, notes the 

 striking resemblance between the Iberg rock and the Devonian 

 limestone at Freiburg in Lower Silesia, which also rises like 

 an island through the overlying Culm greywackes and shales. 



The dimensions of the Lower Devonian series are not 

 known, but the Middle Devonian beds have been found in 

 the Bockswiese mine north of Clausthal to have a thickness 

 of about 100 feet (30 m.), and the Upper Devonian Kramen- 

 zelkalk and Cypridina shales a thickness of 525 feet (160 m.). 

 My best thanks are due to Professor von Groddeck, who has 

 kindly supplied me, since leaving Clausthal, with these 

 figures, as well as with other information which I was unable 

 to obtain during my residence there. 



c. Culm, or Lower Carboniferous. 

 The Culm is developed on the Upper Harz only, where it 

 forms the plateau on which Clausthal is situated, and ex- 

 tends round the west end of the mountains by Seesen to 

 Langelsheim. It is subdivided thus : 



,n \\ Upper or G-rund greywacke. 



^ '' I Lower or Clausthal gi-eywacke, thickness at least 1300 feet. 



(2.) • * Posidonomyenscliiefer " and Culm limestone, 425 feet, 



SKieselschiefer with adinole beds. Whet slates, greywacke and len- 

 ticular limestones, resting conformably on the Upper Devonian, 

 100 feet. 



(1.) The kieselschiefer, or lydian stone of the Harz, is a 



1 von Groddeck, Jahrbuch der konigl. preuss, geol. Landesanstalt, 1882, 

 p, 55. 



