0 7 /» 
O/ O 
THE MEDITERRANEAN NATURALIST 
the upper portions near the junction with the 
Greensands. 
Sulphate of lime in the form of selenite occurs 
also in considerable quantities. It is generally 
found in the Clay in isolated masses of varying 
size and shape, or in aggregations of small crystals 
that have grown round organic remains: these 
crystalline masses usually present a very lamellar 
or fibrous appearance. As a fertilizing agent their 
advantages are fully appreciated by the Maltese 
agriculturist, and it is partly to the abundance of 
selenite in the Marls and Clays that Malta and 
Gozo owe their luxuriant crops of clover and 
cereals. 
A characteristic of the upper portions of the 
Clay-formation is the presence of yellow, ochreous 
nodules, of clay, the majority of which are ovoid 
or subspherical in shape: they are genera lly much 
flattened above and below. When these nodules 
are split along their bedding-planes the perforations 
of Pholades are revealed, and often the casts of 
the Pholades themselves are found within. Similar 
nodules, consisting of indurated blue clay, are 
equally abundant in the lower divisions of the 
Clay. In both varieties the laminae show distinct 
evidencies of stratification, and they always occur 
lying parallel to the flattened surfaces of the 
nodules. 
Prof. Leith Adams alluded to these nodules as 
being derivative (1); but, considering the nature 
of the clay of which they are composed and the 
many of them at any rate are indigenous to the 
formation in which they are found, and that they 
owe their origin to concretionary action due to 
the mutual attraction of the clay-particles one for 
the other. In connexion with this point it is im- 
portant to note that the chemical composition and 
the mineralogical constitution, as well as the fossil 
contents of the nodules, are similar in every 
respect to that of the Clay in which the nodules, 
occur. 
According to the chemical analyses made by Dr. 
John Murray, (1) the different bands of the Clay 
(1) Quart. Journ. Geol. Soc. XXXV. ( 1879) p. 
dl'.); and 'Notes of a Naturalist in the, Nile Valley 
and Malta,’ Edinburg , 1870, p. 131. 
(3) 'The Maltese Islands , etc.’ Scot . Geogr. Mag. 
voL VI ( 1800 ) fK UO, 
vary greatly in their composition. These analyses 
I have repeated, and from them it is demonstrable 
that the proportion of calcium carbonate in the 
yellow and the dark blue clays ranges from 0 to 
10 per cent., in the light blue varieties from 22 to 
40 per cent., and in those parts where the Clays 
graduate into the underlying Gloligei Um-Iimestone 
as much as 67 per cent, of calcium carbonate lias 
been detected. This carbonate of lime is made up for 
the most part of the tests of foraminifera and the 
discs of coccoliths, coccospheres and rhabdoliths. 
Small quantities of phosphoric acid and traces 
of magnesia were also found, by Dr. Murray in 
several specimens of Clay from Gozo. The magne- 
sia is more distinctly preceptible in the rock of 
the upper horizon immediately beneath the Green- 
sands, a fact which I am inclined to think may be 
due to the decomposition of glauconite (silicate of 
iron and magnesia), a mineral which occurs very 
plentifully in the Greensands. 
The following table shows the extent of the 
quantitative variations of the several components 
of the rock: 
Carbonate of lime 2 to 67 per cent. 
Sulphate of lime 4 to 30 ,, 
Carbon, of magnesi ...faint traces to distinct traces. 
Phosphate of lime ....traces to 2 per cent. 
Alumina 25 to 58 per cent. 
Oxides of iron ....4 to 10 ,, 
Residue insoluble in 
dilute hydrochloric 
acid .3 to 10 „ 
The uppermost Clays are very compact and 
impermeable: they therefore form the water- 
bearing stratum of the Islands. 
I\ T . The Oeoanio Remains. 
Organic remains are well represented in the 
Clays, both genericaliy and specifically, but they 
are not equally abundant in every part of that 
formation. Prof. Leith Adams, (3) alluding to 
thjs subject, expressed an opinion that the fossils 
in the Clays are as numerous as those in the 
overlying ancl underlying rocks; but with this 
conclusion I cannot agree, for, despite the large 
: number of genera and species, the number of 
individuals falls far short of that contained in 
any other of the Maltese formations. 
(3) Quart. Journ. Geol. Soc. XNXV . (1870) p. 
1 a 10 et seq. 
