402 Geological Memoirs, 



The next step in the investigation involved the examination of 

 specimens of pumice and similar volcanic rocks from the Royal 

 Mineralogical Collection at Berlin, which is exceedingly rich in 

 various departments of scientific mineralogy, and here the author first 

 turned his attention to the Manilla specimens, partly on account of 

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

 because from this locality an infusorial polishing slate had already 

 been brought by Prof. Meyen. The result of this examination was 

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

 object sought for was neither everywhere present in the same form 

 nor everywhere manifest without some trouble, even when it existed 

 in that form. Under such circumstances it appeared that a special 

 examination might be necessary ; the Manilla tuff, however, did not 

 exhibit any infusoria. 



Although however this was the case, M. Meyen' s collection fur- 

 nished a pumice from Santiago in Chili, marked ' Tollo,' and fully 

 described in his i Travels' (vol. i. p. 338). This pumice forms a 

 steep and almost isolated hill 300 feet high, near the volcano Maipu, 

 at whose foot lies Tollo, 3600 feet above the sea. In this pumice the 

 author found three species of siliceous-shelled infusoria. 



Further investigation showed that a rock at Arequipa in Peru, 

 near the volcano, and described by M. Meyen as being probably 

 a decomposed porphyry, was in fact a true infusorial polishing slate. 

 Several decomposed porphyries are also mentioned as occurring in 

 this neighbourhood, one of which is a hard specimen about five 

 inches in length, from Cangallo near Arequipa,* from which as 

 many as eighteen species of siliceous-shelled infusorial animalcules 

 and twelve species of Phytolitharia have been obtained. Of these, 

 two of the latter group are identical with those found at Santiago, 

 but the third is not among the thirty Arequipa species. 



The author considers it right to add that he has examined several 

 specimens of pumice without finding in them infusorial remains, but 

 he states that the trouble and difficulty of recognising them was at 



* This spot is 7753 feet above the sea, and is a volcano, which, according to 

 Meyen has never erupted lava, but always pumice. 



