64. H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
crateret) to exert sufficient pressure to rend the flanks of the moun 
tain. This lava must have either been within a cone of eruption, 
or possibly a lava lake (?). 
It would be reasonable to suppose that these dykes were formed 
gradually, allowing a certain amount of cooling and escape of vapour 
before appearing at the surface; so permitting the fluid rock to 
issue more quietly as lava, and only forming a light scoria compared 
with the preceding products. 
The breccias of Period 4, Puass III., render these remarks as to 
the sequence of eruptive forces somewhat more complicated. This is 
the outcome of the question :—By what method were these breccias 
deposited, and how is their extraordinary localized thickness to be 
accounted for? Were they the result of direct ejective force, we 
should expect their distribution to be much more uniform; besides, 
we might look for the admixture of some primary eruptive matter 
with them. Possibly this may be represented by masses of new- 
looking scoria which occur in moderate quantity intermixed with 
the breccia, and which might be the ejectamenta of a central cone 
of eruption (?) of the later part of Puasz III. It is true, the 
gradual passage upwards of Period 3 to this may slightly support 
such an idea. 
On the other hand, the thick masses we see in the Vallone di 
Pollena and the neighbourhood seem to point to some great baranco 
draining a craterial hollow, whose crumbling walls furnished the 
materials that were transported along one such gorge and deposited 
in their present position. Of course a baranco playing such a réle 
is not incompatible with the presence of a cone of eruption occupying 
the centre of the craterial plain. What the real condition of things 
was it is impossible to say, and at the most we can only make a 
rough conjecture. The presence of a cone of eruption seems more 
acceptable than a lava lake, but the matter requires further investi- 
gation. 
Puase V. 
General Description.—In the Vallone Sanseverino, overlying the 
lava, occur 90 centimetres of brownish earthy soil, containing 
pieces of scoria and broken lava at the bottom. In the Valloni St. 
Patrizio, di Pollena, and Grande (di Massa), the top of the leucilitic 
breccia is capped by from half to one metre of yellow-brown soil, 
of the same composition as the finer matter of the breccia itself. It 
contains a few fragments of lava much decomposed. The breccia 
eradually blends with this yellow soil. The matter proves, on 
examination, to be nothing more than a more advanced state of 
decomposition of the materials composing the bed below. This 
same deposit may be seen in the cupa between the Vallone di 
Pollena and Vallone Von Buch, reposing on the intrapumiceous 
lava. Both the last locality and the section of the Vallone San- 
severino can give us a correct idea of the exact age of this bed. 
Remarks.—This bed has all the characters of an old vegetable 
soil, and denotes a considerable period of tranquillity separating the 
