644 



POMPEII— INFUSORIAL TUFF. 



[Ch. XXV. 



removed ; although. Lippi took advantage of this removal, 



ument of his antagonists by requiring them 

 to prove the fact. No stream of lava has ever reached 

 Pompeii since it was first built, althou 



+ 



Somma 



streams of which, with tuff interposed, had been cut through 

 in excavations. 



>/ 



• • 



most singular and un 



expected discovery was made, in 1844-45, by Professor 



Pomp 



many 

 . He 



they were, in great part, of organic and freshwater origin, 



consistin 



of the siliceous cases of microscopic infusoria. 



mor 



exam 



between organic life and the results of volcanic activity. On 



conglomerate 



made 



(or rather Diatomacese), invisible to the naked eye and often 



half fused.* No 



mass of this kind, mor 



thick, at Hochsimmer, on the left bank of the Rhine, near 

 the Laacher-see. Some of these Rhenish infusorial accumula- 

 tions appear to have fallen in showers, others to have been 

 poured out of lake-craters in the form of mud, as hi the 



Brohl valley. 



In Mexico, Peru, the Isle of France, and several other 

 volcanic regions, analogous phenomena have been observed, 

 and everywhere the species of infusoria belong to freshwater 

 and terrestrial genera, except in the case of the Patagoman 

 pumiceous tuffs, specimens of which, brought home by Mr. 

 Darwin, are found to contain the remains of marine animal- 

 cules. In various kinds of pumice ejected by volcanos, the 

 microscope has revealed to Professor Ehrenberg the siliceous 



* Not a few of the organic bodies, are now regarded by botanists as plants, 

 called by Ehrenberg ' infusoria,' such and are called Diatomacese and Des- 



as Gallonella and Bacillaria, once sup- midiae. 

 posed to belong to tho animal kingdom, 





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v. 



fi 



b 







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nndertrr 

 .dred e 



v COI 



mav 



j — 



resembling the mass incumbent upon Pompeii and closely 

 connected with extinct volcanos, are now ascertained to be 



ll. p 



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