M. Von Buch on Volcanos and Craters of Elevation. 197 



globosus, figured by Goldfuss, Plate xlii. fig. 9, which I have 

 also found in limesione near Syracuse. The Cardium edule from 

 the Somma is also to be seen in the collection of Dr Pilla. 

 These facts seem quite sufficient to prove, that all strata of tufFa 

 are not thrown out directly from a volcano, but that they are a 

 marine formation^ similar to the tertiary limestone, and that, on 

 that account, they are equally distributed over the whole sur- 

 face. 



Since the Somma pierces through and elevates the strata of 

 tufFa, it cannot, of course, have existed as a mountain previously 

 to the formation of the tufFa. Still volcanic activity was not 

 on that account entirely without perceptible operations in this 

 district. It is remarkable, and in the highest degree worthy of 

 attention, that the tufFa of the Hermit's Hill, and also the strata 

 in the valleys called the Fossa Grande and the Fossa della Ve- 

 trana, contain between the fragments of pumice many blocks 

 and pieces of leucitophyre. In the tufFa of Naples there are 

 no traces of that substance. It would be important to know at 

 what distance from the mountain the leucitophyre is no more 

 found, but such investigations have never been undertaken. 

 These pieces must therefore belong to the strata which were at 

 first spread over the submarine surface by volcanic agency, and 

 which were at a later period raised up as walls of the crater of 

 elevation. But, associated with them, and also surrounded by 

 and included in the tuffk, we find masses of dolomite and other 

 rocks of older formation, which contain the greater number of 

 those beautiful crystals, by which Vesuvius has become more 

 celebrated among collectors of minerals than any other moun- 

 tain in the world. It has been calculated, that of all the mi- 

 neral species known, more than the half occur on the declivities 

 of Vesuvius, and that by much the greater number of these be- 

 ' long to the fragments met with in the tufFa. They are gene- 

 rally termed the ejected masses of Vesuvius; and though we 

 have no examples of such masses having been thrown out from 

 the volcano, yet it has been imagined that they have been so at 

 an earlier period. It becomes quite evident how erroncH)us, 

 nay how completely absurd this opinion is, when wc reflect that 

 the including tufFa is identical in its formation with that of Ca- 

 pua and Naples, and that it was spread around previous to the 



