346 Mr. PouLETT Scrope on the Volcanic District of Naples. 



more numerous. The upper parts are also porous and cellular; while the inte- 

 rior of the rock is as compact, hard, and crystalline as granite. Indeed this 

 stone is quarried for ornamental purposes, — such as columns, — taking an ex- 

 cellent polish, and when worked up being- scarcely distinguishable from gray 

 granite. Irregular fissures divide it into rude prismatic masses. Blocks of a 

 dark-coloured and dense pumice, of porphyritic pitchstone, and pearlstone of 

 a dull greenish colour, occur among the ejected fragments strewn over the 

 outer slopes of the cone. 



One of the most interesting products of the chemical processes which are 

 continually carried on by Nature in the Solfatara, but which has not to my 

 knowledge been described by any of its visitors, is the abundance of globular 

 concretions formed of concentric laminae, which are created in the decomposed 

 trachyte, evidently by the exertion of the affinities of some of its elementary 

 molecules, to which the disintegration of the rock gave the requisite freedom 

 of action. Other globular concretions, but of a more simple structure, (piso- 

 lites,) are common in the loose conglomerate of this and the other neighbour- 

 ing hills, and owe their origin most probably to drops of rain falling on very 

 finely comminuted volcanic ashes, and uniting them into spherical globules ; 

 a pha3nomenon that happened before my eyes on the surface of Vesuvius, 

 during the rains which followed the copious showers of ashes thrown up by 

 that volcano in October 1822. The Solfatara is recorded as having been in 

 eruption A.D. 1180; and, if this account is to be credited, the present crater 

 of this hill must have been produced at that late epoch. This idea is cer- 

 tainly supported by the great heat still evolved with the vapours from its 

 bottom, and also by the occurrence of a small bed of a light and scoriform 

 trachytic lava, of recent aspect, on the summit of Monte Olibano, resting 

 upon the strata of loose tufa which cover the principal mass of trachyte. 

 The whole hill in this case must have possessed a somewhat different figure 

 from the present, when it bore the name of Colles Lc.ucogei, though that 

 name, and the early celebrity of its hot mineral springs, prove its phaenomena 

 to have but slightly, if at all, varied in the interval. 



Next perhaps to the Solfatara in recentness of origin, we should rank the 

 small hill called Capo-mazza, a cone of great regularity occupying the interval 

 between that hill and the Monte Barbaro. It has a circular but shallow crater 

 at the summit, nearly filled, indeed, by the washings from the very friable strata 

 which encircle it. These, as well as the whole substance of the hill, consist 

 of a loose conglomerate, composed of extremely silky, light, and fibrous pu- 

 mice, and its detritus. Similar fragments are scattered thinly on the surface 

 of the Monte Barbaro and the other neighbouring hills, covering a vegetable 



