250 Professor Sedgwick and Mr, Murchison on the 



must differ essentially from that of the other extreme where it graduates into schist. When alternating 

 indefinitely with schist and limestone, the trappean materials are less abundant than the fragments de- 

 rived from the other submarine deposits with which the igneous materials are mixed up*. The calca- 

 reous matter (often in glandular and concretionary forms) may partly have resulted from contempora- 

 neous springs highly charged with carbonate of lime, and may, in part, have been derived mechanicallv 

 from the beds of limestone with which the schaalstein is so intimately associated. 



The schaalstein occupies bold cliffs on the banks of the Lahn near Wetzlar, 

 Weilburg and Limburg. (See PI. XXIII. fig. 9.) Between the two last-mentioned 

 towns it may be studied in all its varieties, alternating with limestone and shale, 

 and broken through at intervals by bosses of eruptive trap which have altered 

 and dislocated the strata. Beautiful examples of the contemporaneous and intru- 

 sive trap rocks, and their relations to the regular deposits, are exhibited in the 

 deep picturesque gorges of the Lahn near Weilburg. 



Limestones of the Lahn. — These limestones, on the whole, appear to be subordinate to the schaalsteins 

 and schists of the tract we are considering, and are of various colours and texture. In their most un- 

 altered condition (e. g. on the north side of the river opposite Limburg) they are dark grey, regularly 

 bedded, sometimes argillaceous, and with white veins. At Carpenheim, near Wetzlar, the rock is seen in 

 very thick beds overlying ferriferous strata, containing in parts small pisolitic and granular iron ore, 

 which are loaded with various shells, including Goniatites. Porphyritic and other igneous rocks appear 

 in the vicinity. 



Fig. 3. 



Left Bank of the Lahn, near Wetzlar. 



Between Wetzlar and Limburg the limestone is found in several patches, some- 

 times with, sometimes without iron ores, which near Weilburg occur in beds ; but 

 in many instances they seem to traverse the strata irregularly, like the masses of 

 iron ore, &c., at Warstein above mentioned. 



The locality at which the limestone of the Lahn has afforded the greatest num- 



* No country offers finer examples than England of contemporaneous and stratified trappean rocks 

 associated with our Devonian, Silurian, and Cambrian systems. Such rocks at one extremity of their 

 mineral types are perfectly crystalline, at the other are brecciated and earthy, and they pass (by every 

 shade of structure and every form of alternation) indefinitely into the aqueous and fossiliferous deposits 

 with which they are associated. Some of these masses (which form an integral part of the highest 

 mountains of Wales and Cumberland, &c.) can hardly be distinguished from the German schaalstein, 

 except perhaps in being (on the whole) more hard and crystalline, and less calcareous. 



