248 Mr Forbes's Physical Notices of the Bay of Naples. 



the sides of the ridge which I have already remarked descend 

 abruptly to the plains. This is more particularly the case at 

 the western side of the hill, where it is so remarkably steep 

 that the road has been carried down by a long oblique tra- 

 verse, where the soft rock is obliged to be so steeply cut 

 away, that every winter accidents happen by the rains. 



This steep and elevated portion of Pausilipo stretches bold- 

 ly into the sea, and the contorted chasms formed in its shores 

 by the waves afford many picturesque subjects for the pain- 

 ter. A little out to sea, in the line of the ridge, and obvious- 

 ly separated from it either by some convulsion of nature or the 

 slow operation of time, rises the small island of Nisida, and be- 

 tween it and the shore a fragment of rock on which a Laza- 

 retto is built. The island is most picturesquely green, and 

 has the appearance from the land of perpetual spring. It is in- 

 teresting in a geological view, from the perfect remains of a 

 volcanic crater it displays, filled with water, and communicat- 

 ing by a breach to the south-west with the sea : it forms the 

 harbour, and is named Porta Pavone. Nisida is composed of 

 tufas, apparently similar to those of Pausilipo, and detached 

 lavas also occur, which may be referred to the eruptions of the 

 extinct crater. A beautiful and characteristic view of the har- 

 bour is given in Hamilton'^s Campi Phlegrcci^ Plate xxii. 



By the fortuitous excavation of the grotto of Pausilipo, a 

 subterranean passage of near half a mile through the heart of 

 the hill, we have the rare advantage of a geological section at 

 a great depth below the surface of the earth. Though in this in- 

 stance it happens that there is almost no variety to be exhibit- 

 ed in the nature of the rock, yet we could not otherwise have 

 been assured of this interesting fact. The darkness of the 

 grotto renders it difficult to examine the structure of the moun- 

 tain ; but Spallanz^ni observes, * that, when viewed by the 

 morning sun, when it penetrates the grotto, the tufa is dis- 

 tinctly stratified, and evidently by the action of water, — a fact 

 now rendered far more distinct by the frequent alternations in 

 the sections on the upper part of the hill. What I believe 

 has sometimes been taken for stratification, is nothing else 

 than the grating of the wheels of vehicles against the sides in 

 * Travels, i. 43. 



