254 Professor Sedgwick and Mr. Murchison on the 



These slates, which take their name from the village of Wissenbach, distinctly rise 

 from beneath the Devonian limestones, repose upon grauwacke, and are quarried 

 on the slopes of the hills which form the southern side of the longitudinal valley 

 in which Wissenbach is situate. 



From the description of the '' schistes argilleux de Wissenbach " by M, Beyrich, 

 we were quite unprepared to find such a beautiful example of slaty cleavage, oblique 

 to the true bedding, as is offered by these strata. So completely, indeed, has the 

 crystalline or slaty impress obhterated the laminae of deposit, that the latter are 

 to be distinguished only by certain undulating and obscure lines, marked by cry- 

 stallized pyrites, and inclined at about 15° or 20° to the S.S.E., while the jagged 

 edges of the slates indicate a cleavage at the high angle of 60°, towards the same 

 point of the compass. It is along these lines of pyrites, which mark the partings 

 of the true beds, that the fossils have been found ; and the workmen, knowing 

 their value, carry them to their houses in the village of Wissenbach, where we 

 purchased a considerable number of them*. 



The first zoological character of these slates which strikes the observer, is the great profusion of Go- 

 niatites. Associated with them are univalve shells (Euomphali, &c.), many Orthoceratites (some of large 

 size), Trilobites of three or four species, &c. 



Besides the valuable collection of M. Dannenberg of Dillenburgt, we examined a series in the mu- 

 seum of Weilburg, collected by M. Sandeman ; and on the last occasion we were accompanied by our 

 friend M. E. de Verneuil. It is from an inspection of all these fossils, as well as from our own collec- 

 tion, that we have come to the conclusion that these slates (underlying, as they do, the Devonian lime- 

 stones of Oberscheld) may be considered to represent the upper beds of the Silurian system. 



The limestones of Oberscheld, near Dillenburg, are clearly identical with those 

 of Elberfeldt (the calcaire a strigocephale of Beyrich), of which we have treated 

 at length when describing the banks of the Lahn ; but the fossils of the underlying 

 slates of Wissenbach (see note, p. 255, and PI. XXIII. figs. G and 7) indicate beyond 

 all doubt the commencement of another zoological type. The profusion of small 

 Goniatites on the one hand might lead us to consider these slates as of younger age 

 than the Ludlow rocks of England ; but the lobes of the species found here partake 

 of the distinction first indicated by Von Buch, of a simple rounded lobe peculiar to 

 the older rocks. Again, we found in this rock specimens of Cyrthoceratites and Or- 



* Appearances of' this kind are not uncommon among the older rocks of England. For example, the 

 fossiliferous slates of Coniston Water Head are intersected by a highly inclined slaty cleavage ; and the 

 true beds (which are much less inclined) are often separated by thin bands of crystallized pyrites. (See 

 Prof. Sedgwick on the Structure of large Mineral Masses, Geol. Trans., 2nd Series, vol. iii. pp. 461, 473.) 



f We are very much indebted to M. Dannenberg, an excellent practical geologist and engineer, for 

 having, on our second visit, made us better acquainted with the structure of the tract east of Dillenburg, 

 extending from the valley of Wissenbach to the mining district of Oberscheld, Sessacher, &c. ; he also 

 furnished us with several good fossils, and a list of the species occurring in each subdivision of the region 

 around the place of his residence, whicii list is given in the next page. 



