Ch. XIV.] 
AGE OF EIFEL VOLCANOS. 
201 
brown coal strata were deposited, was drained ; for the disap- 
pearance of that great body of fresh water may naturally be 
supposed to have taken place when the country was undergoing 
great changes in its physical geography. 
Beds and large veins of quartz are found in the Hundsruck, 
Taunus, and Eifel, the nearest mountain-chains which border 
this part of the Rhine, and their degradation may have sup- 
plied the quartz found in this gravel called Kiesel gerolle by 
the Germans. 
It has been supposed by some writers that the latest volcanic 
eruptions of the Eifel and Rhine coincided in epoch with the 
deposition of the Loess before described (chap. xi.). Such an 
association, if established, would give a comparatively recent 
date to the most modern igneous eruptions ; but I looked in 
vain for any clear indications of such a connexion, and all the 
sections which I saw appeared to indicate the posteriority of 
the Loess. The integrity of the volcanic cones is, for reasons 
before explained, a character to which we attach no value. 
We have, therefore, in this region, graywacke covered by 
brown coal, and some volcanic formations so blended with the 
latter as to prove the igneous eruptions to have been contem- 
poraneous. Yet when we endeavour to assign a chronological 
position to any one part of the series by reference to organic 
remains, we discover that the evidence is vague and inconclu- 
sive. I have as yet been unable to obtain satisfactory proof 
that any one species of fossil animal or plant has been found 
in the brown coal, or superimposed formations which was com- 
mon to a tertiaiy group of known date in any other part of 
Europe ; whereas the reader will bear in mind that the relative 
age of different tertiary formations, of which we have before 
spoken, was usually determined by reference to a comparison of 
several hundred, often more than a thousand, species of testacea*. 
* A memoir has lately been communicated to the Geological Society of Lon- 
don, by Mr. Horner, on the geology of this district. For fuller details consult 
No'eggerath's Rheinland Westphalen, and the works of Von Dechen, Oyen- 
hausen, Von Buch, Steininger, Van der Wyck, Scrope, Daubeny, Leonhard, 
and Hibbevt. 
