248 Dr. Daubeny on the Geology of Sicily. 
also, from this locality, the cast of a shell which resembles an 
arca. 
‘At Cape Passero, however, the fundamental rock is not of 
Neptunian, but of Volcanic origin. At the level of the sea, 
and rising to a considerable height on the cliffabove, is a tuff, 
the basis of which is a species of dark indurated clay, allied 
to wacke, and the imbedded portions are composed partly of 
compact, and partly of cellular lava. 
_ This tuff, as the aggregate may be called, is often ame 
loidal, little spherical concretions of calcareous spar being 
disseminated through it, and in these cases I have observed, 
intermixed with the wacke, numerous crystals of a mineral of 
the hornblende family, which I believe to be schiller spar. 
In other cases the calcareous matter has penetrated uniformly 
into the interstices of the rock, and cemented together its 
arts. 
eT his volcanic tuff is covered towards the summit of the cliff 
by a bed of limestone, which extends to a httle island aes 
site, on which the Castle of Cape Passero is erected. The 
limestone is very different in its external characters from that 
which I had followed from Terranuova. It is of a more crys- 
talline and compact structure, bearing a much nearer resem- 
blance to 1 ie limestones of the older strata, than the pre- 
“ts usual colour is white, but is sometimes veined with blue, 
forming, in appearance at least, a kind of breccia. 
The shells it contains are numerous, numulites are abun- 
dant, as are also madreporites and melanites. But the most 
‘remarkable petrifaction is the hippurite, first discovered I 
believe by Thompson, 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. : . pes 
_. 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 an- 
other volcanic rock similar to the preceding one, and two or 
* My friend Mr. Delabeche, who is just returned from Jamaica, 
me some specimens of tertiary rocks from that island, which, © 
co! 
sh 
yoint of compactness, quite equal those of Cape Passero. 
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