582 Dr. H. J. Johnston-Lavis—The Ponza Islands. 
resisting the powerful scirocco breakers. It seems to me that these 
lavas issued by some lateral fissure in the old cone, and piled them- 
selves up at this point, just as many of the eruptions of lava of 
Vesuvius may have been observed to do during the last ten years, 
just resembling in fact the guttering of a candle. 
The volcano then seems to have remained inactive for some time 
during the deposition of (384), but during that inactivity at the 
surface, the magma immediately below was gradually assimilating 
water, or in other words rising in elastic tension. This eventually 
overcame the overlying obstructions, and a series of explosive 
eruptions followed, interrupted by periods of repose (84-28). 
Whether these explosions drilled out a great crater or craters in the 
old cone, or were at some distance, is not possible of determination ; 
but it is not improbable that the ruin of the dolerite cone had been 
in part brought about. 
Bed (28) seems to show that repose did not follow the last of the 
explosions, but that the eruptive action continued, and as a con- 
sequence dwindled into a state of chronic activity, probably repairing 
in part or wholly, the old cone, during which time fine ash and 
lapilli, now red clay and lapilli, covered the surface (26). At any 
rate, a dyke forced its way to the surface, and gave rise to a small 
scoria cone, from which one or more lava streams poured forth. 
This scoria cone is seen on both sides of the island, and I give in 
Figs. 1 and 2 its relative position to the pumice-beds and the old 
lavas. Fig. 3 is a diagram showing how it is probably cut by the 
present cliff. 
Nn ent re. 
eo pel es Xe 
IN = = 
yay) 
sli fi a ~ 
Fic. 1.—Srction oF A Votcantc Conz And Turrs N.E. oF THE PIANO DEGLI 
OLIvE AT ISLAND OF VENTOTENE. 
35. Submarine reefs of amygdaloid lava. 
34-28. Pumice and other explosive eruptive products. 
27. Doleritic scoria and lavas forming a small volcanic cone. 
x. Dyke which probably supplied same. 
26-8. Upper pumice and other explosive eruptive products. 
7-4. Compact tufa. 
3-1. Vegetable soil, blown sand, etc. 
a, b. Sea-level. 
