244 Professor Sedgavick and Mr. Murchison on the 



the Refrath and Gladbach groups, that some of its subordinate parts may have been 

 repeated over again by undulations, so as to convey a deceptive notion of its total 

 thickness. Without the help of fossils it would have been impossible to attempt 

 any classification of this great formation ; by their help it becomes a most instruc- 

 tive example of the Devonian system of the provinces on the Rhine, and, as we 

 think, of its passage into the Silurian system. For the illustration of the Testacea 

 which abound in these deposits, we refer to the additional memoir and description 

 of our companion M. de Verneuil, and of his coadjutor M. d'Archiac. (See Plates 

 XXV. to XXXVII.) 



Devonian Rocks in Nassau, S^c. (Map, PI. XXIV. and PI. XXIII. 

 Sections 6, 7, 8, 9 and 11.) 



The grand duchy of Nassau is occupied to a considerable extent by the strata 

 of the age intermediate between the carboniferous and the older grauwacke rocks. 

 These strata assume different lithological characters in different districts ; their 

 more peculiar features seem invariably to be derived from their association with 

 igneous rocks. In the mining country around Dillenburg, so celebrated for its 

 ores of iron and copper, the deposits have some lithological features in common 

 with the altered strata near Brilon and Meschede. But in this district the order 

 of the deposits is not inverted, all the stratified masses being seen to dip in regular 

 order to the S. or S.S.E. ; and though much expanded by alternations with schaal- 

 stein, and in parts altered and obscured by bossgs of eruptive rock, the following 

 succession in descending order is observable. (See PI. XXIII. Sect. 6 and 8.) 



1st. Psammitic, thinly laminated schists and sandstones, having a character intermediate between coal- 

 sandstones and slate-clay. These beds are charged with impressions of minute plants, and, on the whole, 

 are not to be distinguished from the " flotzlehrer sandstein " of Von Dechen, which we have shown to 

 represent one of the lower members of the carboniferous group*. Beneath and associated with these 

 beds are finely laminated black schists, loaded with PosidordcB, and containing also some flattened 

 Goniatites, small Orthoceratites, minute Trilobites, and a few Terebratulce. Thin courses of black limestone 

 are detected at intervals (particularly at Erbach, near Herborn) ; and kiesel schiefer is there also present. 

 Thus, from the lithological and zoological characters, there can be no doubt that, in conformity with our 

 views, the whole represents the lower members of the carboniferous system. (See the Tabular List of 



* M. Stifft has the merit of having shown that these peculiar rocks near Herborn " were posterior to 

 the grauwacke," asserting that they are sometimes even unconformable to the schaalstein, which invari- 

 ably underlies them. These beds, including the schists of Herborn, are well described by him as alter- 

 nating with greenstones, and as being, at the points of contact, altered into " kiesel schiefer," horn-stone, 

 " eisen-kiesel," &c. Becher, after whom the Posidonia Becheri is named, considered these beds to be 

 grauwacke ; and the name is preserved by Stifft, although he assigns several lithological reasons for 

 assimilating them to the Jlotzlehrer sandstein of Von Dechen, or the rauch-sandstein of Horel. 



