4, Dr. L. Adams on the Geology of the Maltese Islands. 
from this bed into the Marl is not so gradual as im the other 
deposits, forming often an abrupt line of demarcation between 
the reddish-yellow freestone and the loose clay. The latter bed 
varies in thickness: in the island of Gozo it is well developed, 
where often a thickness of from 40 to 50 fect is discernible; in 
other situations it thins out to a few feet. The fossil remains 
of the Marl are apparently not so numerous or so well preserved 
as in the other formations. Casts of shells are common, and 
often incrusted with iron, which, in the same form as just de- 
scribed, strews the bed in great abundance, together with quan- 
tities of lamellar gypsum. The Marl is a grey or drab-coloured 
clay, more or less tenacious, with lighter-coloured bands running 
horizontally throughout the bed. Passing upwards, we find a 
gradual passage into the Sand-bed, which is composed of a black 
or green-grained glistening sand, intermixed with grey-coloured 
caleareous particles or a reddish sand; the latter is at once cha- 
racterized by the enormous numbers of the littke foraminiferous : 
shell Heterostegina depressa, which is met with in great abund- 
ance throughout this bed and the lower part of the one above it. 
The thickness of the Sand-bed, like the last, is very variable. 
In Gozo cliff, sections of 50 feet in thickness are not uncom- 
mon; but on the south-west coast of Malta it seems to thin out 
to a few feet. The fossils of the Sand-bed are both numerous 
and very well preserved. Teeth, bones, &c., of Delphinus are 
common. The Squali are well represented. Among the Mol- 
lusca, beds of Ostrea Virleti and O. Deshayesti are common ; 
also beds of Terebratula ampulla, var. sinuosa, Brocchi, and 
Megerlia truncata. Among the Echinodermata, Clypeaster altus 
and C. marginatus are very common. 
The passage from the Sand-bed to the Upper Limestone is 
usually gradual; sometimes it merges into a red- and black- 
grained Sandstone (i.e. Heterostegina-bed), then into a red or 
white limestone abounding in Corallines and characterized more 
or less by the quantities of Rhynchonella bipartita, Terebratula 
ampulla, var. sinuosa, and Argiope decollata. The last-named 
variety usually passes into a white calcareous sandstone, either 
compact or soft and porous, but always abounding in casts of 
Pecten, Trochus, Arca, Haliotis. The upper portion of this bed 
is usually an open-grained coarse rock, containing fissures and 
cavities lined with calcareous incrustations. The absence of the 
Squali from the middle and upper parts of the Upper Limestone 
we have repeatedly remarked; whereas such Echinoderms as 
Brissus latus, Brissopsis Duciei, and Clypeaster Redii have been 
hitherto only met with in this bed. 
The thickness of the Upper Limestone varies; its average is 
calculated at 100 feet; but some portions far exceed that mea- 
