404 Geological Memoirs. 



cules, which under the names of porcelain earth, volcanic ashes, sili- 

 ceous sinter, polishing slate, niammillated slate, semi-opal and de- 

 composed porphyry, have been considered, and generally without 

 sufficient reason, as having a direct relation to the volcano. Such 

 is the case in the Isle of France and the Isle of Bourbon with the 

 porcelain earth and volcanic ash ; and also near Cassel, near Cayssal 

 in the Puy-de-D6me and in the Caucasus, and is recognised again 

 in the case of the polishing slate near Bilin, where the polishing and 

 mammillated slate and semi-opal are found, and at Arequipa in Peru 

 with the rock described (but falsely) as decomposed porphyry. 

 Other similar deposits however, as for instance that at Luzon near 

 Manilla, that near Mexico, and those near Eger and Franzensbad, 

 appear to have no reference to volcanic action ; and to this class also 

 belongs the recently discovered polishing slate of the Laacher-See. 



Of the infusorial deposits however, which are distinctly the result 

 of volcanic activity, and have sometimes been brought up and erupted 

 from great depths, we have several examples: — 1st, that of Hoch- 

 simmer near the Laacher-See (perhaps not erupted, and only exposed 

 to the action of heat) ; 2ndly, the trass of the Brohl Valley (suppos- 

 ed by those on the spot to be the site of an ancient volcanic eruption), 

 and the similar beds from Lummerfeld ; 3rdly, the tuff of Civita 

 Vecchia near Rome ; 4thly, the pumice of Tollo, near Santiago in 

 Chili, belonging to the Maipu volcano ; 5thly, the pumice from 

 Kemmerbuhl near Eger ; 6thly, the marecanite tuff near Okhotsk ; 

 and also, 7thly, the same rock at Moya near Quito. 



6. At Hochsimmer there is also a formation resembling phonolite, 

 the component parts of which have the closest relation with siliceous- 

 shelled animalcules. 



7. It is extremely remarkable, that in all the various instances, 

 whether in Europe, Africa, Asia or America, in which microscopic 

 organic bodies are seen to exist in direct or approximate relation 

 to extinct or active volcanic action, all of these belong exclusively 

 to fresh-water formations.* 



8. It appears to result from this review of the phsenomena, either 

 that in the great depths beneath the surface there are ancient de- 



* In the subsequent part of this article it will be seen that an exception to 

 this has been found. 



