264 Professor Sedgwick and Mr. Murchison on the 



Rhine. In the tracts north of Siegen and Olpe, bosses of porphyry and green- 

 stone protrude at several points. At Bilstein, N.E. of Olpe, the porphyry throws 

 off the fossiliferous strata thus : 



Fig. 6. 



Bilstein. 



Shell; Sandstone. 



v_. 



Porphyry. 



To the south of the Aggerthal, the mining country near Runderoth is surrounded 

 by trappean rocks. According to our friend M. Erbreich, this tract contains arena- 

 ceous flagstones and hard dark-coloured limestones (like those we saw in Agger- 

 thai) ; but so contorted and minerahzed, that the traces of bedding are often lost, 

 and the intervals between the masses are filled with great deposits of iron ore. To 

 the south-west of this tract are the celebrated Sieben-Gebirge, forming the most 

 marked eruptive centre of the whole region, concerning whose basaltic and trachytic 

 rocks volumes have been published*. In the districts of the Lahn, but particularly 

 on its southern bank, the protrusions of porphyry, greenstone, &c., are most abun- 

 dant ; and, as before said, they are accompanied by numerous springs of mineral 

 waters. The quartz rocks of the Taunus, which form the boundary of this mine- 

 ralized region, represent upon a great scale that which is seen repeatedly in smaller 

 areas — the conversion of arenaceous strata into quartz rock. This change we 

 consider, in common with M. Von Buch, as due to plutonic agency. 



In a country so much perforated by igneous matter, which has in many places 

 communicated a new mineral impress to whole districts, we are prepared to 

 admit any change, however great, from the original position of the strata. In 

 the second part of this paper, we shall allude to the great inclined basins of Liege, 

 and to the methods employed by Professor Dumont of deducing the original 

 order of superposition from the symmetrical arrangement of the groups up a 

 horizontal section. This method might be applied in Northern Westphalia. But 

 in certain parts of Nassau, where the formations are contorted on a great scale 

 and often inverted — shattered by the protrusion of countless trappean rocks, and 

 so mineralized that the very beds can no longer be distinguished — buried under 

 tertiary deposits or covered by alluvial drift, — in many such places it would, we 

 believe, defy the most patient observer to collect the disjecta membra of the coun- 

 try, and arrange them in any approach to symmetry. 



* See Professor Noggerath's works ; also Mr. Horner's Memoir on the neighbourhood of Bonn, 

 Geol. Trans., 2nd Series, vol. iv. p. 433 et seq., 1836. 



