C. CROSSLAND—-FORMATION OF SHORE-CLIFF NEAR ALEXANDRIA. 113} 
exposed rocks of the Cape Verdes does not occur here. Jointed 
“‘Coralline” is very abundant everywhere on the outside of the 
incrustation. 
Specimens of this growth, even those collected within a hundred yards 
of each other, show differences in the constituents and the proportions in 
which they occur. 
There are two species of Vermetus: a smaller with long tube often largely 
free from the substratum, and a larger with shorter tube forming a coil 
adpressed to the substratum. The former is the more important here, 
and is the important organism of the Cape Verdes; the latter occurs usually 
near high-tide mark and does not often enter into the incrustation, though in 
some cases it forms the bulk of the mass. 
The proportion of sandy tubes of Sabelliformia and Terebellidee is an 
important point, as they are a cause of weakness. They do not generally, 
however, occur in so high a proportion as to destroy the coherence of the 
whole when maceration removes their binding material. 
The proportion of Serpulid tubes, of several species, is always high, often 
forming fully half the whole mass. Nullipore, as noted above, is low. Hence 
the comparative weakness of the whole in comparison with the Cape Verde 
material, which consisted of the two strongest ingredients practically alone. 
The contrast would be far greater but for the abundance of boring sponge and 
annelids in the latter locality. 
That the shore platform owes, if not its existence, at least its definite edge 
to this growth is self evident, but a remarkably clear case is afforded by the 
rocks photographed and shown in PI. 3. fig. 2. Ata point abouta mile east of 
the Palais station on the Ramleh Railway, 2. ¢. about 5 miles east of Alexandria, 
the rock is both higher and harder than usual on this coast, though formed of 
the same broken shell material. The headland thus resulting projects into 
comparatively deep water and is exposed to the full force of the waves. 
The photograph was taken during the retreat of a wave, and shows very 
clearly the extremely regular shelf which borders the rocks. The form of 
the rocks above water-level should be noticed. They show clearly the same 
weathering which is so characteristic of the ‘ Coral-Rag” of the Tropics, and 
at this level they have taken on the same extreme hardness. 
