236 Mr. PouLETT Scrope on the Geology of the Ponza Isles. 



In the case under consideration, if we assume that the graystone of Ponza, 

 Ventotiene, and San Stefano, belongs to the same period, which their nearly 

 equal state of preservation seems to authorize, (and perhaps the analogous 

 formations of Procida, Ischia, and the Phlegraean fields may be referred to 

 the same age,) the superposition of this rock in Ponza to the trachyte, which 

 shows signs of previous degradation, will warrant the inference that the latter 

 rock is of very early date. Its connection with the transition limestone in 

 Zannone conveys no information as to its age, and the conclusion that might 

 appear to follow from the absence of any intervening secondary or tertiary 

 strata^ is destroyed by the fact that they are equally wanting above the tra- 

 chyte. 



The question therefore as to the absolute age of this trachyte is involved in 

 complete obscurity. 



