540 TERTIARY VOLCANIC ROCKS. [Ch. XXXL 



The fishes of the brown-coal Dear Bonn are found in a bituminous 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, Asjnus, 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. This gravel is very distinct in char- 

 acter 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 geography 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. I have before 

 hinted (see p. 123), that this intercalation of volcanic matter between 

 beds of loess may possibly be explained without supposing the last erup- 

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

 deposition 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, resem- 

 bling 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 hap- 

 pened when the country had acquired nearly all its present geographical 

 features. 



Neicer volcanos of the Eifel. — Lake craters. — As I recognized in the 

 more modem volcanos of the Eifel characters distinct from any pre- 

 viously 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 



nology be adopted, I would strongly urge the necessity of referring the Hemp- 

 stead beds of the Isle of Wight and the Limburg strata to one and the same 

 period, whether it be named Lower Miocene or Upper Eocene. 



