Ch. XIV.] 
TRASS OF RHINE VOLCANOS. 
197 
occurs the Pulvermaar of Gillenfeld, an oval lake of very 
regular form, and surrounded by an unbroken ridge of frag- 
mentary materials, consisting of ejected shale and sandstone, 
and preserving an uniform height of about one hundred and 
fifty feet above the water. The side slope in the interior is 
at an angle of about 45°; on the exterior, of 35°. Volcanic 
substances are intermixed very sparingly with the ejections 
which in this place entirely conceal from view the stratified 
rocks of the country *. 
The Meerfelder Maar is a cavity of far greater size and 
depth, hollowed out of similar strata ; the sides presenting some 
abrupt sections of inclined secondary rocks, which in other 
places are buried under vast heaps of pulverised shale. I 
could discover no scoriae amongst the ejected materials, but 
balls of olivine, and other volcanic substances are mentioned as 
having been found f . This cavity, which we must suppose to 
have discharged an immense volume of gas, is nearly a mile in 
diameter, and is said to be more than one hundred fathoms 
deep. In the neighbourhood is a mountain called the Mose- 
berg, which consists of red sandstone and shale in its lower 
parts, but supports on its summit a triple volcanic cone, while 
a distinct current of lava is seen descending the flanks of the 
mountain. The edge of the crater of the largest cone reminded 
me much of the form and characters of that of Vesuvius. 
If we pass from the Upper to the Lower Eifel we find the 
celebrated lake-crater of Laach, which has a greater resem- 
blance than any of those before-mentioned to the Lago di 
Bolsena, and others in Italy — being surrounded by a ridge of 
gently sloping hills, composed of loose tuffs, scoriae, and blocks 
of a variety of lavas. 
Trass and its origin. — It appears that in the Lower Eifel 
eruptions of trachytic lava preceded the emission of currents 
of basalt, and that immense quantities of pumice were thrown 
out wherever trachyte issued. In this district, also, we find 
* Scrope, Edin. Journ. of Sci., June 1826, p. 145. 
f Ilibbertj Extinct Volcano? of the Rhine, p. 24. 
