212 Proceedings of the Boyal Physical Society. 



The Hercynian Eocks are thus classified : 



/ V X TTT- 1 t- • r \ Upper (Graptolithensclnefer zone). 



(2.) Lower Wiederschiefer, . . j ^ower (Kalk-Grauwacken zone). 



(1.) Tanner Grey wacke, . . . Oldest rock of the Harz. 



(1.) The Tanner greywacke is usually fine grained, and 

 occurs in thick beds with thin shaley intercalations. It 

 contains plant remains, Knorria, Sagenaria, Lepidodendron, 

 Archceocalamites, and, according to Kayser, some corals and 

 crinoid stems. 



(2.) To these rocks succeeds the lower division of the 

 Lower Wiederschiefer. This group consists of shales, with 

 greywacke beds containing plants ; also whet slates, kiesel- 

 schiefer,^ and lenticular fossiliferous limestones, which are 

 sometimes of workable thickness. The limestone is of two 

 kinds — a compact splintery siliceous variety, and a granular 

 sparry variety. The former is characterised by containing 

 cephalopods, and the latter by its brachiopods. The fauna is 

 Devonian, and is represented in the genera Gyroceras, Gonia- 

 tites, Cryphaeus, Terehratida, Spirifer, Amplexus, and Pleuro- 

 dictyum. 



The whet slates, or " Wetzschiefer," are yellowish or 

 greenish-grey homogeneous silicified clay slates, with micro- 

 scopic mica scales, yellowish-green microliths, tourmaline 

 needles, and sometimes abundance of garnets.^ The Kiesel- 

 schiefer will be noticed under the Culm Eocks. 



The Upper or Graptolite shale group consists of clay slates 

 charged with crinoids, orthoceratites, and, towards the top of 

 the series, with graptolites, which have not been found on 

 any other horizon in the Harz.^ It is interesting to note 



1 "Schiefer" in German relates to geometrical form, and is applied to a 

 great variety of rocks with a lamellar, tabular, or flakey structure, due either 

 to bedding or to cleavage (Schieferung). Thus: Thonschiefer (clay slate), 

 S chief erthon (argillaceous shale), Dachschiefer (roofing slate), Glimmer-, 

 Hornblende-, etc., schiefer (mica-, hornblende-, etc., schist), Kieselschiefer 

 (flinty shale), Kupferschiefer (copper shale), etc., etc. The German language, 

 so often more expressive than the English, is in this case less so, 



2 H. Credner, Elemente der Geologic, 4th edit, 1878, pp. 108, 119. 



^ See K. A, Lossen, Zeitsch. d. d. geol. Ges., Bd. xxi., p. 284; Bd, xxvi., 

 p. 206; xxvii,, p. 454. E. Kayser, Die Fauna d. altest. Devon Ablagerung 

 d. Harz, p. 210, 



