Structure of the Volcanic Projectiles. 
29 
shows the great dust-cloud ascending and curiously branching as it 
attains a height above the crater about equal to the height of the 
mountain. (See Plate I., Fig. 1.) The interval between eruptions varied 
from three to four minutes to a half hour. 
From Vulcanello we visited Mr. Narlian’s ruined villa (about three- 
fourths mile from the crater), which presented a most desolate appear¬ 
ance with its smashed and charred roof and walls half buried in ashes, 
lapilli and bombs. The vine and fig plantation was almost completely 
buried in cinder and entirely ruined, occasioning a loss of about £40,000 
sterling. The entire plain (Atrio) between the mountain and the encir¬ 
cling ring of Monte Saraceno and Monte Luccia, is covered with lapilli 
to a depth of several feet, and this is strewn with projectiles (the so- 
called “ bombs ”) of all sizes from such as are smaller than one’s fist to 
those several feet or even yards in diameter. The larger ones have dug 
themselves great pits in the loose lapilli so that they are nearly or quite 
buried, the lapilli being thrown out to a considerable distance. When¬ 
ever the mass was more than afoot in diameter it was sure to be cracked 
or broken from the force of its fall, being composed of a coarse acid 
pumice. Their porous character explains how they could attain to 
such extraordinary dimensions. We saw numerous specimens that 
had clearly been over four feet in diameter and at distances of 
one-half to three-quarters of a mile or more from the crater. 
Mr. Narlian mentioned one near the well of his house that he 
thinks was ten yards in diameter. This I did not see. A projectile 
at least three feet in diameter we found well up on the slope of Monte 
Saraceno in the encircling “ Somma.” The structure of these projectiles 
is very interesting. Their shape approaches roughly to an ellipsoid and 
generally one of rotation, though they are really polyhedral with peculiar 
warped plane surfaces. Pear-like shapes are not found and their presence 
would hardly be expected when the material is so porous. They have an 
outer glassy skin, about a half-inch thick, with fine scattered vesicles. 
This has a gray surface color like pumice, with cracks opened in and be¬ 
tween the warped bounding surfaces. Dr. Johnston-Lavis has aptly termed 
this unique structure the “ bread-crust structure,” since it closely resem¬ 
bles both in appearance and in probable manner of formation, that of a 
baked bread crust, in which cracks have formed from the expansion of the 
gas in the dough after the surface has hardened. The larger cracks show 
upturned edges and reveal at the bottom of the crack a fine-grained 
spongy pumice. Everyone will recollect analogies to this in bread. 
The interior of the “bomb” is pumice with in general an increase 
in the size of the vesicles toward the center.' (See Plate I, Figure 2.) 
These vesicles are usually elongated in the direction of the radi- 
vectori of the bomb. This is doubtless to be ascribed to the centrifugal 
force developed by the rotation of the mass in the air. The petrograph- 
