Ehrenberg on Infusoria in Igneous Rocks. 399 



in the same manner. Similar formations were observed by the 

 author to be still in progress, but the great mass of the deposit con- 

 sists of the mere empty infusorial cases. Scarcely less extensive 

 than these are the deposits of massive carbonate of iron in the 

 neighbourhood of the acidulous springs, which commonly, but not 

 always, contain fragments of Gaillonella ferruginea. In the midst 

 of the true siliceous infusorial earth there also occurs phosphate of 

 iron in the form of blue vivianite, above which the fen-mud appears, 

 and is often quite filled with and hardened by the black iron 

 pyrites. 



Here howeffer it will be seen that neither the mineralogical nor 

 the physiological conditions are wanting for the combination of the 

 materials, and the black pyrites is manifestly a local and subsequent 

 formation. Whether indeed the sulphates of soda and lime in the 

 water have received the excess of carbonate of iron after the forma- 

 tion of the pyrites, or whether the Gaillonella ferruginea has ab- 

 sorbed sulphuric acid given off after death by the bodies of the sili- 

 ceous-shelled animalcules, the author leaves it to other naturalists to 

 determine, but he expresses his belief that the vast multitude of 

 microscopic animalcules at Franzensbad have had a direct and im- 

 portant influence on the local peculiarities observed in that neigh- 

 bourhood. 



By such investigations the volcano in the neighbourhood came to 

 be viewed in a new light. It rises from the plain with a gentle 

 inclination on the eastern side, but to the west there is a nucleus 

 of cellular basalt or basaltic lava-slag rising to the summit; the 

 formation in the neighbourhood is mica-slate. The whole of the 

 eastern dome-shaped slope forms a stratified heap of light volcanic 

 erupted ashes, often containing lumps of some size and also very 

 small fragments of mica-slate, quartz, or white pumice. The im- 

 pression made by viewing these phsenomena was, that the eruptions 

 of cellular lava and slag, and consequently the whole slope of the 

 hill, consisted of nothing more than a valley or the bed of a lake 

 of volcanic origin, which existed before the outburst of lava, but that 

 the valley was not destroyed by the eruption, and received no eleva- 

 tion. Several experiments were made with a view of confirming this 

 impression, and with regard to the stratification of the ashes it 



?, F 



