530 Dr. H. J. Johnston-Lavis— The Ponga Islands. 
(q) Ivregular finely peccostonally) brecciated yellow earth ; probably an old 
concretionary soil 1:00 
(r) Ochre-stained pumice ; the upper ten centimetres are less stained, have 
larger fragments with pyroxene crystals and ejected blocks ... ane Ogu) 
(s) Brown earth with concretions, finer at the top and passing down into 2°60 
(¢) Same as last, lighter in colour with intermixed ieee which at some 
spots forms a band es Ses 2a fae ane an on odeo0 
(«) White dust not concretionary ... 900 ire wide 0 ec eOROU 
(v) Brown pumice a ea te see anOk2D 
(w) Pumice bed with lapilli and few ej jected blocks ... a 309 soa ZOD 
(2) White pumiceous dust-bed .. one goo Pile) 
(y) Pumice-bed with light buff concretionary ‘dust-bed in middle... ne) 18a) 
a White pumiceous dust-bed .. a8 Be 908 Bees 10°) 
(zz) Trachyte forming main mass of the island. 
The main body of the island is composed of a mass of trachyte 
which seems to have oozed forth as a compound dome. The flow 
arrangement resulting from this is well shown as the rock exhibits 
a distinct pipernoid structure. Doelter has fully described?’ this 
rock both from a chemical and microscopical point of view, but 
says little of the overlying strata of pumices, lapilli, dust and earth. 
These all point to a considerable number of explosive eruptions in 
the vicinity, as there are no signs of a crater of explosion visible on 
the island itself. That during the deposition of these tuffs the 
island was above the water is proved by the numerous vegetable 
soils, roots preserved by concretions, surface erosion, ete. That the 
explosive eruptions extended down to the metamorphosed limestones 
beneath the volcanic platform from which occurred the explosive 
eruptions is proved by the few ejected blocks met with in the tuffs. 
The ejected blocks also include lava fragments like the underlying 
trachyte and the dolerite of Ventotene, but most interesting is a 
leucitophyre, no massive remains of which have been discovered in 
the islands. The latter, nevertheless, is another addition to the 
widely-distributed localities of Italy in which leucite forms an 
important rock constituent. Loose blocks have been found in tuff 
at Procida, but so far leucite rocks have not been recognized in 
Ischia or the Ponza group of islands. 
Ventotene is also exceedingly interesting, as the continuous cliff 
section stretching round it clearly reveals its structure. The follow- 
ing is a compound section of the island, beginning from the most 
superficial deposits :— 
M. 
(1) Vegetable soil, rich in snail shells = 
(2) Blown sand of. powdered sea shells with many snails, chiefly H. Cantiana. 
It is very full of concretions . 4:00 
(3) Brown earth with concretions especially at bottom, often with bands of 
blown sand coo 0D) 
(4) Compact yellow tuff, used for carving into portable “furnaces, passes 
down to... : 4 to 7:00 
(5) Compact grey dust and pumiceous s scoria with bands of loose pumiceous 
scoria in the middle : 208 a 360 ae soa WOK 
(6) Scoriaceous pumice with pieces of lignite ve ace 296 soo | OROS) 
(7) Lapilli consolidated in patches ues abs apo) P20) 
1 See Doelter, “ Carta geologica delle Isole Dae Pa Ve e Zannone,”’ Roma, 
1876. —Memorie per servire alla descrizione della Carta Geologica d’ Italia, vol. iii. 
Parte 12, 1876. 
