Ehrenberg on Infusoria in Igneous Rocks. 395 



afterwards became the receptacle of a similar deposit. This it was 

 thought might go on until a more powerful and energetic upheaval 

 of the bottom of the crater either gave to these strata a steep inclina- 

 tion or fairly lifted the concave bed into a convex dome, thus pre- 

 cluding any further repetition of the process. It appeared, indeed, 

 from an examination of its internal structure, that the hornstone- 

 like and glassy semi-opal was not formed immediately by volcanic 

 agency. 



Two other cases in which microscopic animalcules were associated 

 with volcanic rocks had also been noticed by the author, but in 

 these the conditions were less distinctly marked than in the former. 

 One of them had reference to the red firestone of the north of Ire- 

 land, which has apparently undergone fusion, and in which some of 

 the chalk infusoria are distinctly present; and the other was the 

 edible earth of the Tungusians, from the Marekan mountains near 

 Okhotsk, of which M. Ermann, jun., had brought specimens. So 

 long ago as in March 1843,* the author had stated that in this 

 edible earth, which appears under the microscope to consist almost 

 entirely of pounded pumice, there were three distinct species of 

 known siliceous Infusoriaf and one of Phytolitharia. J M. Ermann 

 considered, from the circumstances under which it occurs, that the 

 edible earth consists of a very fine, dry and meagre dust of pounded 

 rock, in which this strange association of infusorial animalcules has 

 unaccountably become mingled ; and the author admitted such an 

 explanation, describing the species as offering a remarkable instance 

 of geographical extension, whatever be the relation in which they 

 stand to the rock or formation. The recent investigations with re- 

 gard to pumice give a new interest to this remarkable fact, and take 

 away from its apparently anomalous character by showing that there 

 is no necessary relation of the organic remains in question to the rock 

 or deposit called Marecanite. With regard to the other instance 

 mentioned, that of the fused firestone, it appeared to possess little 

 general interest, since the rock containing the remains might easily 



* Monatsbericht, p. 104. 



f Fragilaria amphicephala, Gaillonella dislans, and Tabellaria vul- 

 garis. 



X Film plantw. 



