80 GEOLOGICAL MEMOIRS. 



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, how- 

 ever, 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 de- 

 scribed in his ' 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 polisl^ng 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 

 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 sub- 

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

 pure infusorial polishing slate, in which thirty-three species of poly- 

 gastric 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, Avhich either, as at Moya in Quito, 



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

 Meyen, has never erupted lava, but always pumice. 



