226 
THE MEDITERRANEAN NATURALIST 
power will be in direct proportion to the amount 
of superheated water existing in the magma; and 
crateriform hollows of ten miles in diameter are 
not difficult of comprehension. In fact, it seems 
somewhat astonishing that such excavations are 
not far greater, when we think of the terrific 
energy that may be stored beneath us in the form 
of such enormous dykes as those great masses of 
diabase in the region of the Hudson river. The 
great difference between the two conditions is, no 
doubt, that the water in the boiler is perfectly free 
to evaporate, whereas in an igneous magma it is 
molecularly scattered through the viscous mass, so 
that although the energy stored in equal quantities 
of water in either condition would be the same, 
the dispersion will be spread over a longer time 
in the case of the paste, due to retardation of 
escape in consequence of viscosity. 
In the author’s recent researches on the past 
and present eruptive phenomena of Vesuvius (1) 
certain important facts were brought out which it 
has been possible to confirm in a large number of 
instances in other volcanoes. When this volcano 
is in a state of chronic' activity, with short 
intervals between one eruption and another, the 
violence with which the ejections take place is 
small compared with what occurs after long 
periods of quiescence. Thus, for instance, during 
the building up of the old mountain, and again 
during the last two to three centuries, we find 
that a very large portion of the products consisted 
of continuous masses of lava, whereas in the 
great explosions that excavated the gigantic crater 
of the Atrio del Cavallo, and which, from the 
interstratification of vegetable soils, and denuda- 
tion marks, are proved to have occurred at long 
intervals apart, are characterized by deposits of 
spongy pumice, with a total absence of anything 
but fragmentary products. But in the above case 
we have not only geological, but even historical, 
proof; for we know that at least for many centuries 
before a.d. 79 this volcano had been apparently 
extinct, and that in the great Plinian eruption we 
had nothing but spongy fragmentary varieties of 
its usual igneous rock. The eruptions that fol- 
lowed the Plinian one occurred at diminished 
intervals, and so the more did their products ap- 
(1) Quart . Jour'll. Geol. Soc., January, 1SS4. 
proach in structure that of the lava of chronic 
activity, until, in the tenth century, pumiceous 
materials formed no longer, at any rate as far as 
the essential ejectamenta go, the products of these 
eruptions. To take another example, the prece- 
dents and whole history of which is pretty well 
known, namely, Monte Nuovo. We find that the 
main mass of the mountain is built up of pumice 
in various stages of comminution; capped, or 
covered, by more compact and crystalline scoria, 
or lava, fragments, which were only ejected at the 
last, when the volcano tended to pass into the 
chronic condition. We also know that such vol- 
canoes as Tomboro, Krakatoa, and others like 
them, after a long quiescence burst forth with an 
amount of violence sufficient to cause disturbances 
throughout our planet, and tnen produce ejecta- 
menta that are always of pumiceous character. 
( to be continued ) 
Tools of the Pyramid- Builders. 
A two years’ study at Gizeh has convinced Mr. 
Flinders Petrie that the Egyptian stone-workers 
of 4000 years ago had a surprising acquaintance 
with what have been considered modern tools. 
Among the many, tools used by the pyramid- 
builders were both solid and tubular drills, and 
straight and circular saws. The drills, like those 
of to-day, were set with jewel (probably corundum, 
as the diamond was very scarce), and even lathe- 
tools had such cuttiug-edges. So remarkable was 
the quality of the tubular drills and the skill of 
the workmen that the cutting marks in hard 
granite give no indication of wear of the tool, 
while a cut of a tenth of an inch was made in the 
hardest rock at each revolution, and a hole through 
both the hardest and softest material was bored 
perfectly smooth and uniform throughout. Of 
the material and method of making the tools 
nothing is known. 
Maltese Caecilianellse. 
A CONTRIBUTION TO THE STUDY 
OF MALTESE LAND SHELLS 
by Alfred Caruana Gatto. 
The only species of this genus mentioned in Dl'. 
Caruana’s Catalogue of the shells of Dir. Mamo’a 
