Ch. XXXI.] LAKE-CRATERS OF THE EIFEL. 679 



shale, called paper-coal, from being divisible into extremely thin 

 leaves. The individuals are very . numerous ; but they appear to 

 belong to a small number of species, some of which were referred by 

 Agassiz to the genera Leuciscus, Aspius, and Perca. The remains of 

 frogs also, of extinct species, have been discovered in the paper-coal ; 

 and a complete series may be seen in the museum at Bonn, from the 

 most imperfect state of the tadpole to that of the full-grown animal. 

 With these a salamander, scarcely distinguishable from the recent 

 species, has been found, and the remains of many insects. 



A vast deposit of gravel, chiefly composed of pebbles of white 

 quartz, but containing also a few fragments of other rocks, lies over 

 the brown-coal, forming sometimes only a thin covering, at others 

 attaining a thickness of more than 100 feet. The gravel is very dis- 

 tinct in character from that now forming the bed of the Rhine. It is 

 called " Kiesel-gerolle " by the Germans, often reaches great elevations, 

 and is covered in several places with volcanic ejections. It is evident 

 that the country has undergone great changes in its physical geogra- 

 phy since this gravel was formed ; for its position has scarcely any 

 relation to the existing drainage, and the great valley of the Rhine 

 and all the more modern volcanic rocks of the same region are posterior 

 to it in date. 



Some of the newest beds of Volcanic sand, pumice, and scoriae are 

 interstratified near Andernach and elsewhere with the loam called 

 loess, which was before described as being full of land and freshwater 

 shells of recent species, and referable to the Post-pliocene period. 

 But this intercalation of volcanic matter between beds of loess may 

 possibly be explained without supposing the last eruptions of the 

 Lower Eifel to have taken place so recently as the era of the depo- 

 sition of the loess. 



The igneous rocks of the Westerwald, and of the mountains called 

 the Siebengebirge, consist partly of basaltic and partly of trachytic 

 lavas, the latter being in general the more ancient of the two. There 

 are many varieties of trachyte, some of which are highly crystalline, 

 resembling a coarse-grained granite, with large separate crystals of 

 felspar. Trachytic tuff is also very abundant. These formations, 

 some of which were certainly contemporaneous with the origin of the 

 brown-coal, were the first of a long series of eruptions, the more recent 

 of which happened when the country had acquired nearly all its pres- 

 ent geographical features. 



Newer Volcanoes of the Eifel. — Lake-Craters. — As I recognized 

 m the more modern volcanoes of the Eifel characters distinct from 

 any previously observed by me in those of France, Italy, or Spain, I 

 shall briefly describe them. The fundamental rocks of the district 

 are gray and red sandstones and shales, with some associated lime- 

 stones, replete with fossils of the Devonian or Old Red Sandstone 

 group. The volcanoes broke out in the midst of these inclined strata, 

 and when the present systems of hills and valleys had already been 



