OF MONTE SOMMA AND VESUVIUS. 95 
The microliths of leucite are difficult to obtain a clear view of ; 
they appear more irregular in form than is generally the case. 
This obscuration is due to a dark brownish-green granular mate- 
rial that seems to be composed of broken-up microliths of pyroxene 
added to a considerable number of irregular ones of magnetite. The 
blackish colour of this scoria seems to depend on this abundance of 
magnetite and pyroxene in a dusty form, just as in its analogue of 
Puase III., Period 2. 
The microscopic inclusions of foreign matters are even more 
common than the macroscopic. 
Remarks.—The year a.p. 471 or 472 witnessed one of the most 
terrible of historic eruptions, almost rivalling that of a.p. 79. It 
is said that ashes fell in various parts of Kurope, and even terrified - 
the people of Constantinople, to which city some ashes reached. The 
eruption is said to have continued for three or four years. 
This record seems to correspond exactly with what it would lead 
us to expect to find in the characters of the ejectamenta, which seem 
to show signs of long duration. 
It appears that the structure and composition of these scoriaceous 
pumices show that the mass was kept boiling up for some time, so 
as to allow of the formation of the large leucite and other crystals. 
At the same time the magma gradually lost its essential volatile 
components, and was by degrees reduced in temperature; for the 
evidence of fracture of the crystals, pulverization of the microliths, 
and envelopment of fragments of other rocks, shows that for a long 
time the mass was kept in a continual state of movement. ‘Those 
portions that were already cooled would be ground and pulverized 
in the crater by the continual explosions, affording those ash-showers 
that disturbed the peace of Europe. From time to time the solid 
or still plastic masses were ejected so as to fall on the outer slopes 
of the cone, on which, during a period of three years, were accu- 
mulated those not unimportant deposits already spoken of. 
Whether this eruption was, at its commencement, sufficiently 
violent to have destroyed the cone which had been formed by 
the small eruptions between a.p. 79 and its date, it is difficult 
to decide; but there seems little doubt that this one, especially 
during its feebler spasms, did much to add to the crater-plain and 
raised up on it a cone of eruption of very considerable dimensions. 
This was probably the most important contribution to the founda- 
tion of the present Vesuvian cone. Of course an exact appreciation 
of the amount of filling of the crater by the products of this erup- 
tion 1s impossible; nevertheless I am inclined to the opinion that 
this did much more than any other eruption during the first ten 
centuries. This opinion is based, first, upon the comparatively 
feeble but prolonged character of this eruptive period ; and secondly, 
upon the large amount of material ejected compared to that derived 
from others during that epoch. 
The igneous magma seems to have originally been moderately rich 
in aqueous matter, "sufficiently so, at any rate, to prevent any thing 
like true lava issuing, unless such streams did not reach beyond the 
