Ehrenberg on Infusoria in Igneous Rocks. 415 



of volcanic ashes, which according to microscopic analysis is clearly 

 shown to be made up exclusively of organic bodies, most of them 

 the siliceous parts of plants, but some of them the remains of infuso- 

 rial animalcules ; and these are not species inhabiting the sea, but 

 are, without exception, confined to freshwater. 



3. According to the result of numerous observations made with 

 reference to various localities in Europe, Asia, Africa and America, 

 it appeared that the relation of microscopic organic bodies to vol- 

 canic rocks was strictly confined to those forms known only as ex- 

 isting in freshwater, and it seems also, as stated above, that this is 

 the case in the island of Ascension, under very striking circumstances. 

 This might have been supposed to arise from the similar marine 

 forms not having been yet observed, or from the mixture of other 

 material at the sea-bottom having rendered the whole more readily 

 fusible, and so not presenting the phaenomenon for investigation. 

 There has now, however, been found a volcanic formation of infu- 

 sorial tuff forming mountain masses in Patagonia, and exhibiting 

 distinctly its marine origin, so that this remarkable appearance of 

 an exclusively freshwater origin is taken away, and the marine forms 

 are fully represented. 



4. In Patagonia this Pyrobiolite rock is developed into a terrace- 

 shaped formation upwards of 800 feet high, greatly resembling the 

 European chalk, although without any trace of carbonate of lime, and 

 containing here and there a considerable quantity of gypsum. It 

 forms apparently one of the largest uniform masses of rock that we 

 know of on the earth, amongst those manifestly due to the same 

 agency throughout and perfectly continuous, and exhibits everywhere, 

 and is perhaps chiefly derived from, the influence of the most minute 

 forms of organic existence. 



5. The Patagonian white tuff, formed perhaps during the sub- 

 marine eruptions of the great Chilian and Patagonian Cordilleras of 

 the south-western part of South America, and possibly the result of 

 the great and uniform activity of the eruptive forces which elevated 

 that chain of mountains, must be of tertiary or yet newer date since 

 the pyrobiolite rock reposes on fossiliferous tertiary strata. It 

 would not be unimportant to subject to careful microscopic inves- 



3 H 



