EHRENBERG ON INFUSORIA IN IGNEOUS ROCKS. 79 



The lower pumiceous conglomerate evidently reposes on the grau- 

 wacke, which with clay-slate forms the underlying deposit in the 

 neighbourhood. The beds of volcanic conglomerate which enclose 

 the infusorial polishing slate have a considerable dip, amounting to 

 20° north-west, and their thickness appears in some places to amount 

 to as much as twenty-four feet, but the bed of polishing slate nowhere 

 exceeds three inches. The upper covering seems to form part of a 

 grey basaltic lava-stream proceeding from Seelsberg. The author 

 was indebted to M. von Dechen for this information. 



A careful microscopic examination gave the following singular 

 results with regard to this locality : — 



First: — Not only is the stratum of polishing slate entirely made up 

 of the siliceous cases of infusorial animalcules, but the beds associated 

 with it, consisting, as we have seen, of volcanic tuff and pumiceous 

 conglomerate, are composed in great part of the same substance. 



And secondly, the tuff and pumice conglomerate exhibit the infu- 

 sorial cases in a distinctly fused condition, resembling that noticed 

 by the author in some investigations made several years ago on in- 

 fusorial earth that had been burnt for tiles or porcelain. 



Thirty-eight species of microscopic infusoria were determined by 

 the author from the Hochsimmer beds, and it seemed probable that 

 many more might be added to the list ; of these species, however^ 

 only two are new, and of the remaining thirty-six, one has hitherto 

 been known in Europe only as a tertiary fossil, but all the rest are 

 living European species. 



Before extending his investigations further in the determination 

 of additional species from this locality, the author thought it advi- 

 sable to advance in another direction, and since the very fragments 

 of volcanic rock themselves had exhibited these organic remains, 

 he availed himself of M. Krantz's collection at Berlin, and selected 

 several different kinds of pumice for examination. He thus ob- 

 tained a number of specimens of volcanic ash or trass from Brohl 

 on the Rhine, and he afterwards also obtained specimens of similar 

 tuff from Civita Vecchia, and from Posilippo near Naples. All 

 these he carefully examined. 



The result A\as very striking, since the nature of the pumice was 

 apparent everywhere, and exhibited not merely that peculiar cellular 

 structure whichrcminds the observerof fused specimens of G^«z7/oy/^//<7, 

 but every minute fragment, even from the very middle of the mass, 

 exhibited more or less distinctly the contained forms, and a number 

 of species was soon added to the list of those contained in pumice. 



Tlie next step in the investigation involved the examination of 

 specimens of pumice and similar volcanic rocks from tlie Uoyal 

 Mineralogical Collection at Berlin, which is exceedingly rich in va- 

 rious departments of scientific mineralogy, and here the author lirst 

 turned liis attention to the Manilla specimens, ])artly on account of 

 the wide extension of the volcanic tuff there said to exist, and partly 

 because from tliis locality an infusorial i)olishing slate had already 

 been brought by Prof. Mcyen. The result of this examination 

 was unexpected, but at the same time instructive, since it taught 



