Ehrenberg on Infusoria in Igneous Rocks. 405 



posits, perhaps of coal, formed under conditions remarkably similar 

 to those now existing ; or else, which is more probable, that these 

 immeasurably great masses of tuff, pumice, trass and mud, erupted 

 from volcanoes, have been sucked in by the volcano from time to 

 time, in the form of existing turf and bog, or fen-mud, greatly 

 assisted perhaps by the vicinity of freshwater lakes and pools of 

 water ; and then having been partially fused are thrown out again 

 during the next eruption. 



9. The invisible portion of the animal kingdom is thus found to 

 possess a new, important and unexpected influence upon the solid, 

 and in this case volcanic portion of the earth, — an influence which 

 invites a closer investigation, and recommends itself to universal 

 attention. 



On the 24th of April 1845, Professor Ehrenberg made another 

 communication to the Academy, stating the result of further investi- 

 gations into the subject, partly with reference to some additional 

 specimens from Hochsimmer, and partly on various volcanic tuffs, &c. 

 from distant localities. 



I. — On the Volcanic Infusorial Tuff (Pyrobiolite) of the Rhine. 



Owing to the active researches of the local authorities, and espe- 

 cially of M. von. Dechen, the author has obtained much new infor- 

 mation with regard to the Laacher-See and Hochsimmer ; and he 

 states that, including a firestone forwarded by M. Noggerath, not 

 less than thirty-nine different kinds of rock had been forwarded to 

 him for investigation. » The geological relations of these rocks he 

 considers it highly essential to record ; and they are the more impor- 

 tant, since other objects had been forwarded to him for examination 

 from distant localities, and a comparison of the results with what we 

 know of the volcanic relations of the inland Rhine district would tend 

 to a completion or rapid extention of our general knowledge of the 

 subject. 



The sections at Hochsimmer are obtained from six points ; and 

 the following account is quoted by the author from a communication 

 he had received from M. von Dechen : — 



