older Deposits of the North of Germany and Belgium. 239 



are in thin irregular courses, and often very highly mineralized. These great litho- 

 logical changes are accompanied by various plutonic rocks, of which there are no 

 traces in the several districts before mentioned. They consist of porphyries, green- 

 stones, and other intrusive masses, in ridges or bands parallel to the strata*. 



With the exception of a few points (where the beds are thrown off by the rocks 

 of igneous origin), the strata of the whole elevated region are seen to dip to the 

 south. Now the strata, which lie to the north of the great limestone, contain 

 black and thin-bedded limestone, and dark-coloured Posidonia shales, and are obvi- 

 ously but the prolongation of the lower carboniferous strata of Westphalia. Yet 

 are these strata overlaid by the great limestone, which, in its turn, is overlaid by 

 the old grauwacke (or Silurian) rocks of the southern mountains. 



It follows, therefore, that the regular order in which we have been enabled to 

 trace these formations through so long a space is here completely deranged, and 

 that all the great groups are absolutely inverted, the older being incumbent on 

 the younger. 



We shall have occasion to speak at greater length upon similar phsenomena on 

 the left bank of the Rhine ; therefore we need do no more in this place than re- 

 gister the facts as they fell under our observation. 



We may, however, remark, that the occurrence of trappean rocks may perhaps 

 suggest the cause of these enormous derangements of position, of the reality of 

 which there can be no doubt : for we can follow the several groups along their 

 "distorted lines of strike till we trace them into the country where they are in the 

 true normal positions indicated in the previous sections. Indeed, in the disturbed 

 district of Brilon, we examined a section indicated by M. Erbreich, in which the 

 lower carboniferous strata, after being reversed, fold over again and dip to the 

 north under the cretaceous rocks (as in the accompanying woodcut). 



Fig. 2. 



General Relations of the Strata N. and S. of Brilon. 



S.S.E. 



Hoppekc. , 



2. Greensand. 6'. Unproductive coal grits and shale. 6+. Posidonia and Goniatite schist. 



7. Devonian beds with iron ore and fossils. 8. Slaty rocks. a. Porphyry, greenstone, &c. 



The figures and letters are those used in the Map to distinguish the formations. 



The abundance of iron ores is one of the most striking consequences of the in- 

 trusion of the porphyritic and greenstone rocks among the Devonian strata ; and 



* The course of these trap rocks, and of a considerable part of the limestone, has been laid down 

 from the original surveys of MM. H. Von Dechen and Erbreich. 



2 I 2 



