98 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
or even of pumiceous scoria, are entirely absent, making a distinctive 
difference between pumice and scoria. 
Remarks.—The continual vomiting forth of igneous matters in 
rapid succession, as occurred in the first four centuries of the Chris- 
tian era, must have expelled all that which had occupied the chim- 
ney or conduits, and replaced it by new material. The short time 
that this new igneous magma would be exposed to hydrating infiu- 
ences would reduce its heat but slightly, and increase its expansive 
power but very little. The result would be a more tranquil state of 
eruption, slower loss of heat, together with an absence of that minute 
vesicular structure due to the interstitial or intermolecular conyer- 
sion of aqueous matter into vapour. Such a temperature, with the 
slight tendency to be broken up by elastic fluids, would render pos- 
sible, or at least be favourable to, the outflow of lava. As a result 
of the above conditions, the fragments of scum blown out would 
have only a coarse cellular structure, and might be very vitreous, 
from the sudden cooling of a material having a very high tempe- 
rature. 
Such seems to have been the case in the present instance. At 
times the eruptive action was so feeble that it ground up the loose 
stones of the crater-walls, and, adding some of its own solidified 
material, simply from time to time expelled the pink sandy lapilli 
that we see forming bands in the scoria. 
A somewhat similar state of things has been very common at 
Vesuvius lately, when in a moderately tranquil eruptive condition, 
as we may there see ejectamenta that approach to a certain extent 
that which we have been describing. 
Tn the eruption of the year a.p. 512 lava is said to have flowed, 
but it is not stated whether it was down the slopes of the mountain 
or within the great crater of the atrio, which it probably was occu- 
pied in filling up. 
So great was the damage done by the ashes and cinders that 
. Theodoric*, the Gothic king, condoned the taxes in the injured 
districts. 
The information given us by the deposits we have just described 
agrees in many particulars with the records of the eruption of the 
sixth century. Procopius, who also chronicled this outburst, de- 
scribes distinctly a deep crater, nearly reaching to the bottom of the 
mountain, in which could be seen lava boiling up. Such a condition 
proves, first, little or no cone of Vesuvius, and, secondly, that the 
eruption could not be classed as of paroxysmal type. Probablythe 
form of the interior of the mountain was terraced, that is, it had 
two concentric craters, divided by a low annular cone or plain. 
Puase VII., Period 6. 
The jast of the deposits exhibited at the Canale di Arena, except 
lapilli and ash from very recent eruptions, is a bed of about 13 metre 
in thickness. It is composed of highly crystalline pumice, remark- 
* «History of the Gothic Wars,’ transl. H. Holcroft, 1653, book ii. chap iv. 
