416 Original Articles. | July, 
beds is due to false-bedding, and not to elevation at all; consequently 
it is no indication of their being older than the horizontal fresh-water 
strata, ‘ 
Again, supposing that the marine beds were the older, they must 
once have filled up the valley. By what manner of water-action could 
they have been so completely washed away that no trace of them 
exists anywhere beneath the fresh-water formation, and only small 
patches are left high up on the hill-sides, where they could least of 
all be expected ? 
Considering all the difficulties in the way of the marine beds being 
the older, and that there is no physical reason why they should not be 
the newer (granting the apparent dip to be due to the false-bedding), 
we may legitimately compare the fossils of the Cos and Xanthus fresh- 
water beds, with the shells figured in the Plate, without taking into 
account their supposed Pliocene age, to which view, it will be found, 
their evidence is entirely antagonistic. It may be remarked, however, 
that if the fresh-water strata are the older, the lowest bed, in which 
occur the same genera as Captain Spratt has obtained from Crete, 
must, according to its fossils, either be very low down in the Upper 
Miocene, or must belong to the Lower Miocene: perhaps it does not 
matter which we consider it; but the point I shall now attempt to 
establish is that our Cretan fossils are of the same age. 
Geological Age of the Fossils under consideration.—A glance at the 
following lists will show that of those from Cerigo, all, with the 
exception of Cerithium Cytherorum (a new species), occur in the 
Upper Miocene of Europe, while two began life earlier. The balance 
of evidence is therefore strongly in favour of the Cerigo fossils being 
Upper Miocene ; that is to say, of the age of the Vienna and Bordeaux 
Basins. The marine formation in Crete, described by M. Raulin, and 
said to be of Miocene age, may possibly belong to the same set of 
strata, though his list does not include any of our species, which are 
less decidedly marine than those enumerated by him. 
The Cretan specimens being, however, all ditterent from those of 
Cerigo, with one exception, require further discussion. Melanopsis 
buccinoidea, the only species common to both sets of fossils, is also 
one of those which appeared first in strata older than the Upper 
Miocene, and with it is associated in Crete Cerithium Lamarckii, 
which began life in Hocene times and extended up into the Lower 
Miocene, but which has not been found in newer strata. On the 
other hand, we have Melanopsis Bouei, representing the Upper 
Miocene period, and a species of Unio, allied to Unio litoralis, which 
tells us very little concerning its age. The remaining species, three 
in number, are new, and one of them presents some remarkable 
modifications of form, so that it is rather difficult to form a correct 
idea of their geological date. 
The genus Unio contains very many species, resembling one 
another so closely as to render it very difficult to distinguish them, 
especially in the fossil state, so that very little reliance can be placed 
on them as indicative of the age of Tertiary strata. Melanopsis 
buccimotdea, as we have seen, furnishes no clue to the age of beds 
