196 OLDER PLIOCENE PERIOD. [Ch. XIV. 



viewing die first of these we recognize the ordinary form of a 

 crater, for which \ve have been prepared by the occurrence of 



No. 50. 



a, Village of Gemunden. c, Weinfelder Maar. 



b, Gemunden Maar. - 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 scoriae, 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 with 

 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 



