262 Dr Daubeny on the Geology of Sicily. 
by Thomson, and noticed in an early volume of the Geological 
Transactions. The entire mass of the rock seems to be charged 
with this shell, which it is difficult, however, to detach. 
The best specimens I succeeded in procuring are already in 
the museum, and may I hope enable Mr Miller to throw some 
light on the structure of this rare and curious fossil. 
The bed of limestone already noticed is covered by another 
volcanic rock similar to the preceding one, and two or three of 
such alternations occur within a few miles of the Cape. After 
this a pause seems to have taken place in the volcanic opera- 
tions, for the calcareous rocks continue without interruption for 
a distance of almost thirty miles northwards of the Cape, to a line 
nearly parallel with the town of Palazzolo, when indications of 
igneous action appear to recommence. 
The most numerous alternations, however, of these two classes 
of deposits occur between the town of Lentini and the Moun- 
tain of Santa Vennera, to which, as illustrating the general struc- 
ture of this district, I shall chiefly confine myself. 
Santa Vennera, the loftiest mountain in the south of the Island, 
is capped with lava, full of cells, having that oval or elongated 
figure common in rocks from which elastic vapours have been 
disengaged, whilst they were flowing in a current. 
Underneath it is a bed of compact limestone, full of minute 
and hardly distinguishable shells. At a still lower level on our 
descent towards Lentini, we meet with a second bed of volcanic 
matter, similar to the first, and before we reach the town two 
other such alternations take place. 
At length, as we descend the last hill, which brings us 
thither, w T e find ourselves on a calcareous stratum singularly 
contorted, and dipping in a direction just the reverse of the 
preceding strata, which seem to be inclined towards the south- 
west. 
The volcanic nature of the beds which separate the calcare- 
ous deposits in this part of the island, being unquestionable, it 
becomes an interesting point to ascertain to what class of forma- 
tions the latter must be referred. 
In this inquiry the order of superposition will assist us little, 
for, as the whole of these beds rest, as we have seen, on the vol- 
canic tuff* of Cape Passero, so are they covered, in the rare in- 
