older Deposits of the North of Germany and Belgium. 229 



some varieties of the millstone grit of England), which are associated with yellowish or light-coloured 

 sandstone and shale ; and the whole series finally rises to the surface in powerful ledges on the banks of 

 the river Ruhr, particularly near Herdecke, Westhofen, and Schwerte, etc. 



In quitting the lower edges of the coal-field, we find these yellowish and light-coloured grits and sand- 

 stones (which here and there contain thin courses of coal and many impressions of plants) to be under- 

 laid by dark grey, slightly micaceous shale, and thin-bedded, hard, grey sandstone, throughout which 

 many small plants are distributed. This formation composes hills several hundred feet high, the strata 

 of which rise up at great angles from beneath the coal-field. Their lowest member is composed of dark 

 shales, which are frequently loaded with pyrites and are much worked in the extraction of alum. 

 This " alaun schiefer " of the Germans constitutes therefore the base of the whole coal tract, from which 

 there is a regular and unbroken sequence upwards, through the beds before described, into the overlying 

 or productive field. The alum shale reposes on the uppermost limestone of this region — the mountain 

 or carboniferous limestone of English geologists (6 + of Map). 



The order here described may be seen in any transverse section from N.N.W. 

 to S.S.E. along the escarpment of the coal-field, whether made at its western ex- 

 tremity or towards its eastern apex. The finest exhibitions of the lower beds are 

 in the wooded hills between Herdecke and Schwerte on the N.N.W, and Hagen 

 and Schelke on the S.S.E. ; and the same order on a smaller scale is found in 

 the sections near Werden and Kettwig. 



In their range to the E.N.E. these lower carbonaceous strata of sandstone and 

 shale become much expanded, and cover a wide area of country to the north and 

 east of Arnsberg, where they pass downwards into the lower calcareous zone to 

 which we have just adverted*. 



To those persons who are acquainted with the structure of Devonshire we can 

 convey no clearer notion of this unproductive or lower coal tract than by saying, 

 that it strikingly resembles the " culm districts " of that county in the colour and- 

 composition of the rocks, and in the abundant occurrence of small grass-like 

 plants ; the species of which, however obscure, appear to us the same in the two 

 countries. This sub-group is the " Flotzlehrer sandstein " of the German geolo- 

 gists, by whom it has hitherto been considered as the uppermost member of the 

 grauwacke series ; a position which it does not occupy, as it is an integral part of 

 the carboniferous system, being superior to the mountain limestone. (See sec- 

 tions PI. XXIII. figs. 1 and 2 ; and the colour 6^ of Map, PL XXIV.) 



Carboniferous Limestone of Westphalia, (Mountain limestone, " Berg-Kalk") with 

 its associated bands of " Kiesel- Schiefer" and bituminous limestone. (Map, 

 PI. XXIV. colour 6 + , and PI. XXIII., Sections 2 and 4, colour d.) 



The coal-field, with its associated inferior strata above described, throughout that 

 part of its course which extends from Cromford near Ratingen to the country north- 

 east of Velbert, is underlaid by a strong band of limestone, which, from its position, 



* Ante, p. 225. 

 VOL. VI. — SECOND SERIES. 2 H 



