216 Mr. PouLETT ScROPE on the Geology of the Ponza Isles. 



much of its original extent. Detached groups of craggy rocks stretch to a 

 considerable distance from both its northern and southern extremities. On 

 the west side rise three or four similar masses, lofty, precipitous, and sepa- 

 rated from the main islet. These and the steep cliffs by which it is girt round, 

 exhibit unequivocal signs of the powerful degradation to which it is exposed, 

 particularly on the western shore, from the superior violence of the swell occa- 

 sioned by the prevailing winds, which blow from that quarter over a vast ex- 

 panse of open sea. This destroying force tends rapidly to separate the island 

 into two nearly equal parts. The opposite indentations which occur towards 

 the middle of its length, called La Forcina and II Porto, are indeed already 

 connected by a narrow channel, practicable to small boats, in the formation 

 of which, however, art appears to have assisted nature. On either side of this 

 channel the island rises to a height of from four to five hundred feet, swell- 

 ing gradually towards the south into a peaked eminence, overhanging a steep 

 cliff of tufa, and situated near what may be supposed the centre of the original 

 area of the island. The northern height forms a steep dome-shaped mass, 

 resembling in its outline the Montagna della Guardia in Ponza. The surface 

 of Palmarola is well wooded, and its appearance, particularly on the western 

 side, extremely romantic and picturesque. It is neither inhabited nor culti- 

 vated, and therefore clothed in the unchecked and exuberant vegetation natural 

 to the climate, and fostered by the richness of the soil. The myrtle, dwarf- 

 palm, and wild-figtree spring up with peculiar luxuriance wherever a few feet 

 of rocky ledge afford them sufficient depth of soil ; while the cytisus, genista, 

 cistus, and numerous tribes of aromatic herbs, occupy every cleft in the 

 craggy cliffs. 



The precipitous shores of this island exhibit the same abrupt and irregular 

 intermixture of the prismatic trachyte and the semi-vitreous conglomerate 

 which has been observed in Ponza. The conglomerate here also, as in Ponza, 

 graduates in every instance into dark bottle-green pitchstone, where it comes 

 in contact with the prismatic trachyte. I could not observe any indications 

 of the siliceous trachyte which forms so large a part of the other island. The 

 prismatic trachyte, however, becomes highly siliceous in many parts, and is 

 universally ribboned with a multiplicity of zones of different shades of white, 

 yellow, blue and brown, varying in compactness and in the proportion oH 

 isilex they contain. These zones are still more constant and remarkable than 

 in the analogous rock of Ponza. Their wavings and contortions on the small 

 as well as on the large scale, resemble those of mica-schist and gneiss. Here 

 also, as in Ponza, there exists every indication of the zones being owing to 

 the rock having been drawn out in their direction while in a half-liquid state. 



