VOLCANIC AGENCY. 123 



showing that the mouth of the river probably opened into this 

 spot ; whilst the higher calcareous beds, which form rubbish- 

 beds, must have been deposited in rather quieter water, seeing 

 that in them some leaves of poplars and camphor-trees again 

 occur. These leaves show that the youngest and uppermost 

 beds belong to the same period as those below them. 



From this description it appears that in the course of time 

 great changes took place in precisely the same spot in the lake 

 of (Eningen, probably occasioned chiefly by the river which 

 opened into the lake, and aided perhaps by a rising and sinking 

 of the ground, which might be due to volcanic agency. Prof. 

 Arnold Escher de la Linth has ascertained that in the bed of the 

 brook below the lower quarry at (Eningen there occurs a very 

 peculiar dark-coloured volcanic rock, which, by its pisolitic 

 grains, its fragments of limestone, and its rounded and angular 

 fragments of blackish fine-grained granite, often as big as a 

 man's fist, resembles the phonolitic and basaltic tuffs of the 

 neighbouring Hohgau. The same rock also occurs on the road 

 between Solenhof and Langenmoos, above and below the level of 

 the upper quarry ; and the dark brown arable clay in the imme- 

 diate vicinity of the upper quarry seems also to indicate a vol- 

 canic origin, and resembles the soil produced from the decom- 

 position of the tuffs of Hohgau. 



The occurrence of these volcanic rocks in the bowl-like en- 

 virons of the quarries of (Eningen renders it probable that during 

 the Upper Miocene period volcanic eruptions here took place, 

 and that, as in the Hohgau, volcanic rubbish accompanied by 

 fragments of limestone and granite were brought to the surface. 

 By the action of these causes the Molassic ground of the region 

 acquired a bowl-like depression, in which water accumulated and 

 a lake was formed. It is manifest that the volcanoes of the 

 Hohgau were in activity at the same time with those of CEnin- 

 gen, as the plants contained in the tuffs of Hohenkrahen agree 

 with those of (Eningen. From the district of Ochsenwang 

 (south of Kirchheim) in northern Wirtemberg Prof. Heer is 

 acquainted with a dark basaltic tuff which is proved to be con- 

 temporaneous with the (Eningian formation by the plants and 

 insects which are contained in it. 



