Ehrenberg on Infusoria in Igneous Rocks. 403 



first exceedingly great. Amongst the instances however in which his 

 labours were rewarded with success was that of a specimen in the 

 Royal Mineralogical Museum, obtained from Mexico, marked ' Tisar, 

 clay-slate and siliceous earth.' It consisted of a white substance 

 from the vicinity of a volcano, and proved to be an almost pure 

 infusorial polishing slate, in which thirty-three species of polygastric 

 infusoria and five Phytolitharia have already been made out. 



These two beds of fossil infusoria from South America and Mexico 

 were the first observed from that locality, and are interesting not only 

 by their direct relation with recent volcanic action, but also because 

 they show the conditions under which we may expect to find the 

 material in which further investigations of this kind may be expected 

 to be successful. 



The following are the general results of his investigations, as stated 

 by the author at the close of his first communication : — 



1. We have presented for microscopic investigation infusorial 

 masses that have been fused by exposure to volcanic fires. 



2. Beneath the fused masses of infusorial remains other masses 

 are found resembling polishing slate, but containing none of those 

 remains elsewhere common, which are capable of being dissipated by 

 exposure to moderate heat. 



3. It appears that from the depths of a volcano masses of organic 

 bodies have been thrown up, which either, as at Moya in Quito, 

 contain imperfectly carbonized vegetable remains, or, in the case of 

 more complete fusion, exhibit similar forms imbedded in pumice or 

 tuff. With regard to the peculiar change produced by fusion, it 

 does not seem possible that the effect can have resulted in any other 

 way, or by foreign organic bodies penetrating the rock while moist, 

 and soon after its formation, since the appearance is peculiar, and 

 can be brought about by artificial means. 



4. Organic remains have not been met with in all kinds of pumice; 

 and only those appear to have been formed out of the infusorial cases 

 where there has been no powerful flux present to reduce the mixture 

 to the condition of glass. It will require further investigation to de- 

 termine the relation of Obsidian to these pumiceous formations. 



5. In the vicinity of many volcanoes which either have erupted or 

 do erupt chiefly pumice, there are great deposits of infusorial animal- 



