540 
ELEMENTS OF GEOLOGY. 
Lower Rhine and the Eifel are coeval with the Lower Mio¬ 
cene deposits to which most of the “Brown-Coal” of Ger¬ 
many belongs. The Tertiary strata of that age are seen on 
both sides of the Rhine, in the neighborhood of Bonn, rest¬ 
ing nnconformably on highly inclined and vertical strata of 
Silurian and Devonian rocks. The Brown-Coal formation 
of that region consists of beds of loose sand, sandstone, and 
conglomerate, clay with nodules of clay-iron-stone, and occa¬ 
sionally silex. Layers of light brown and sometimes black 
lignite are interstratified with the clays and sands, and often 
irregularly diffused through them. They contain numerous 
impressions of leaves and stems of trees, and are extensively 
worked for fuel, whence the name of the formation. In sev¬ 
eral places layers of trachytic tuff are interstratified, and in 
these tuffs are leaves of plants identical with those found in 
the brown-coal, showing that, during the period of the accu¬ 
mulation of the latter, some volcanic products were ejected. 
The igneous rocks of the Westerwald, and of the mountains 
called the Siebengebirge, consist partly of basaltic and part¬ 
ly 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 feldspar. 
Trachytic tuff is also very abundant. 
M. Von Dechen, in his work on the Siebengebirge,'^ has 
given a copious list of the animal and vegetable remains of 
the fresh-water strata associated with the brown-coal of that 
part of Germany. Plants of the genera Flabellaria^ Ceano- 
thus, and Daphnogene^ including I), cmnamomifolia (Fig. 
155, p. 239), occur in these beds, with nearly 150 other plants. 
The fishes of the brown-coal near Bonn are found in a bitu¬ 
minous shale, called paper-coal, from being divisible into ex¬ 
tremely 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 Leu- 
ciscus^ Aspms^ and Perea. The remains of frogs also, of ex¬ 
tinct 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 distin¬ 
guishable from the recent species, has been found, and the 
remains of many insects. 
Upper and Lower Miocene Volcanic Rocks of Auvergne.— 
The extinct volcanoes of Auvergne and Cantal, in central 
France, seem to have commenced their eruptions in the Lo wer 
* Geognost. Beschreib. des Siebengebirges am Rbein. Bonn, 1852. 
