19G 
OLDER PLIOCENE PERIOD. 
[Ch. XIV. 
viewing the first of these we recognize the ordinary form of a 
crater, for which we have been prepared by the occurrence of 
No. 50. 
a, Village of Gemunden. c, Weinfelder Maar. 
b, Gemunden Maar. i ; ; d, Schalkenmehren Maar. 
scoriae scattered over the surface of the soil. But on examin- 
ing the walls of the crater, we find precipices of sandstone and 
shale which exhibit no signs of the action of heat, and we look 
in vain for those beds of lava and scoria?, dipping in opposite 
directions on every side, which we have been accustomed to con- 
sider as characteristic of volcanic craters. As we proceed, how- 
ever, to the opposite side of the lake, and afterwards visit the 
craters c and d, we find a considerable quantity of scoriae and 
some lava, and see the whole surface of the soil sparkling witli 
volcanic sand and ejected fragments of half-fused shale, which 
preserves its laminated texture in the interior, while it has a 
vitrified or scoriform coating. 
We cannot, therefore, doubt that these great hollows have 
been formed by gaseous explosions ; in other words, that parts 
of the summits of hills composed of sandstone and shale were 
blown up during a copious discharge of gas or steam, ac- 
companied by the escape of a small quantity of lava. It is a 
peculiar feature of the Eifel volcanos that aeriform discharges 
have been violent, and the quantity of melted matter poured 
out from the vents proportionably insignificant. In this re- 
spect they differ, as a group, from any assemblage of extinct 
volcanos which I have seen in France, Italy, or Spain. 
In some of the Eifel lavas, as in Auvergne and the Vivarais, 
fragments of granite, gneiss, and clay-slate are found inclosed ; 
pieces of these rocks having probably been torn off by the 
melted matter and gases as they rose from below. 
A few miles to the south of the lakes above-mentioned 
