62 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
lava is the same as that of the lower. The pyroxene and large 
magnetite are of the usual type. ‘The biotite differs only in its size, 
and, as in the lower flow, contains crystals of sanidine. The latter 
mineral occurs as crystals very neatly and sharply terminated. 
There is also some triclinic felspar. The magnetite microliths are 
smaller than in the lower lava, but still are of a greater size than 
in the ejectamenta of Puasr III. The microliths of pyroxene are 
the same as in the lower lava; the sanidine crystals are larger, 
with brush or forked ends. 
Remarks on Puaszs III. ann IY. 
In the Vallone Sanseverino and the Vallone Von Buch, if we trace 
up these streams of lava to their origin, we find them terminating 
near masses of scoria, which, seen in section, are in some places 
20 metres or more in thickness, and occupy exactly the same strati- 
graphical position as the lavas. This maximum development occurs 
in the first-named valley near the 375th contour-line, and near 
the 475th in the Vallone Von Buch, in which part of the scoria 
may be seen in the section to overlie the lava belonging to Period 1, 
though beneath this there is a thin layer of scoria. 
One of the most striking features of these scoria-deposits is the 
great suddenness with which they make themselves apparent inter- 
calated in the section, the rapidity with which they increase to their 
maximum thickness, and then as rapidly decrease and disappear. 
Again, we find them thinning out laterally in the same abrupt 
manner. Thus, in the Vallone Pietri Pomice, the next valley to the 
left of Sanseverino, this scoria is from 3 to 5 metres thick opposite 
the maximum development in its neighbour, and, like it, soon dies 
out as we ascend and descend the valley. The same remark applies 
to the Vallone di Pollena, where there are only a few centimetres of 
scoria to show the rapid thinning out of the curious deposit so 
largely developed in its neighbour, the Vallone Von Buch. 
Such an arrangement could not have been the product of an 
eruption from the central vent, since this would be much more uni- 
form in its distribution ; and it would be impossible thus to explain 
the usual absence of the scoria in sections where the beds imme- 
diately above and below come in contact, the latter showing no signs 
of erosion. | 
Again, I have never been able to trace the lavas of this epoch 
higher up the valley than these scoria heaps. If these streams 
had flowed from the great crater-lip they surely would have been 
accompanied by explosive action, distributing a certaim amount of 
fragmentary material generally, which, as has been remarked, only 
exists, on the contrary, in these very localized spots. The peculiar 
characters of the scoria, which can be seen to have been deposited 
directly in its present site while in part plastic, combined with other 
features already mentioned, all point to one very distinct and almost 
certain inference. 
We have, in fact, to deal with parasitic cones bursting forth on 
the slopes of the voleano, from which issued scoria, lapilli, ash, and 
streams of lava. 
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