Professor Silliman's Geological Notes. 141 



Geological Notes. By Professor SiLLiMAN, Junr. 



Professor Silliman, junr., during his late visit to Europe, ex- 

 amined many interesting geological localities, of which he 

 gives short notices in his Journal. Some of these we now 

 lay before our readers. 



1. Grotto del Cane and Lake Agnano. 



The Grotto del Cane, or dog grotto, has been so much 

 cited for its stratum of carbonic acid gas covering the floor, 

 that all geological travellers who visit Naples feel an interest 

 in seeing it. Unfortunately, like some other grottos, its en- 

 chantment disappears on a near view. It is a little hole dug 

 artificially into the foot of a hill facing Lake Agnano. The 

 aperture is closed by a door, and the space within is barely 

 sufficient for one persori to stand erect. Into this narrow 

 cell a poor little dog is very unwillingly dragged and placed 

 in a depression of the floor, where he is soon narcotized by 

 the carbonic acid. The earth is warm to the hand, and the 

 volume of gas given out is very constant. 



Lake Agnano, as is well known, fills the bottom of an an- 

 cient crater whose walls are still to be distinctly traced. On 

 the shore of the lake immediately opposite the Grotto del 

 Cane, there is a constant and copious discharge of carbonic 

 acid, and the water of the lake at that part is in great agi- 

 tation from' its escape. Nor is other evidence wanting of the 

 present operation of the ancient causes which have charac- 

 terised this region. At the foot of the hill, on the east, are, 

 numerous vents of steam and sulphur. Over some of these va- 

 pour baths (Sudatorise) have been established, which site held 

 in some repute in cases of rheumatism. Digging a short dis- 

 tance into the hill, near the ruins of the villa of Lucullus, it is 

 easy to perceive the presence of volcanic energy in the hot 

 vapours, accompanied with sulphur, which issue copiously 

 from the surface. The villa of LuciJlus was entirely buried 

 in lapilli and volcanic ashes, proceeding, as is supposed, 

 from a vent in the immediate neighbourhood ; but from 

 which vent does not appear — evidently not from the one 



