NOME VIII. VOLCANIC GLUTENITE. ,511 



well preserved as if they had lately been pre- 

 pared. See what I have said of this curious 

 variety of trass of the environs of Andernach, 

 vol. i. p. 24, of the Annales du Museum. Spal- 

 lanzani found a similar charcoal in a tufo of the 

 isle of Lipari. See also vol. iii. p. 11, of Spal- 

 lanzani's Voyage to Sicily. 



" Of the particular configuration peculiar to 

 some tufos. 



<c Note. It must be observed, that under some 

 circumstances tufos, particularly those which 

 owe their origin to the concurrence of fire and 

 water, have undergone a recession which has 

 given them a prismatic form. I have seen si mi- jf r "^ 

 lar ones, but in small quantities, in the extinct 

 volcanos of Habischwakl, near Hesse Cassel. 

 The most remarkable of this kind are those of 

 Campania, near the town of St. Agatha, also 

 between Mounts Sarchio and Vitolano, near a 

 place called La Varrettella : but the largest and 

 the best formed are those which are found on the 

 road to Venafro, near the bridge of Calm and 

 the tavern of Torricella. 



* c Chalcedonic substances are sometimes found Chalcedony. 

 in tufos, which seem to be the result of a second- 

 ary formation, such as those of Pont-du- Chateau, 



