THE MEDITERRANEAN NATURALIST 
132 
shore cliff's. This variation in the colour of the 
strata, is due in a great measure, to the varying 
states of combination of the iron that pervades 
them. 
The gradations from a cold-grey to a yellowish 
hue through which the various divisions of the 
bed pass, are due to the extent to which this 
admixture takes place. Dr. Dawson, in a paper 
read before the Geological Society (I) advocates 
the view that the colouration of rocks is due 
to the decomposition of iron pyrites and that the 
sulphuretted hydrogen produced by the decay 
of organic matter acting on the sesquioxide 
converts it into bisulphide, and thus a colouring 
matter is formed; and further researches con- 
ducted by other well known scientists seem to 
support this hypothesis. (2) 
There are, however, some cases among the Mal- 
tese rocks which Dr. John Murray considers 
admit of a simpler explanation. It is his opinion 
that the original colour of the whole cf the 
formation, was a dark-blue; and that the colours 
that the rockjjias now assumed are the result of the 
oxidation of the iron pyrites, that it originally 
contained. He says “While these rocks are, for 
the most part, of a reddish or yellow colour, 
along the cliffs on the coast, and in the cutting for 
the New Dock, there are large, more or less, 
circular bluish patches, and it is noticed, that these 
blue patches are removed to the greatest distance 
from faults and fissures. In the bluish, or grey- 
coloured upper-beds, and even in the over- lying 
blue clay itself, the rocks on each side of a fissure 
have a red colour, the thickness of this reddish 
band on either side of the faub or fissure being 
less, as a rule, the more the bed contains. 
The microscopic section of the red rocks and 
the blue patches show no difference, so far as 
concerns the organisms, but the blue patches 
contain iron pyrites, which is absent in the red 
rock through oxidation, the iron pyrites often 
filling the for aminif era and forming casts of the 
shells. 
(1 ) Quart. Journ. Geo. Soc. Vol. XXXIII. Ji- 
ll I 
(2) Dr. Sterry Hunt. Quart. Journ. Geo. Soc. 
June 1859. J. W. Young “ Chemistry of Carbo- 
niferous., and Old Red Sandstones I 
It thus appears more than probable, that these 
blue patches will ultimately disappear with further 
oxidation; indeed it is evident to me, that at the 
time these Globigerina rocks were first raised 
above the sea, they were all of a blue colour, and 
that the red colour is entirely due to subsequent 
oxidation, the more porous calcareous bed having 
been oxidised at a more rapid rate, than those 
containing a large quantity of clayey matter.” 
Interstratified with the beds of this formation 
are several seams, or layers of phosphatic nodules, 
that consist, for the most part of aggregations 
of brownish masses, together with a great abun- 
dance of the phosphatised remains of mollusca, 
echinoderms, corals, whales, dolphins, sharks, 
rays, seals, turtles and other creatures; the whole 
being firmly bound together by the fine calcareous 
matter, that was rained down upon them from the 
waters of the ocean above. 
All of them, when broken, will be found to 
contain an organism, around which the phosphatic 
matter has segregated. 
The fossilised remains of the contained orga- 
nism, too are generally of a brownish biack hue, a 
condition, that is probably owing to the combina- 
tion, either of the phosphoric acid contained in 
the organism, or that derived from the animal 
remains around, with the iron contained in the 
rock. 
It is to the phosphate of iron thus formed, that 
the change in their original appearance is due. 
These nodules seams often attain a thickness of 
from 2 to 3 feet; and, at least one of them extends 
throughout the length and breadth of both 
islands. 
A remnant of one may be seen at Tignk point 
marking the transition between the Globigerina 
Limestone, and the Lower Coralline Limestone; 
while another, of considerable thickness may be 
seen on the shores of St. Paul’s Bay, 
In some localities, these seams are entirely 
absent, and in others they thin out from a thick- 
ness of two and three feet to as many inches. 
The cliffs at Marsa Scala, at the Gozo light- 
house, at Dueira, and at Fouim-er-Rih, offer 
every facility for a close examination. 
At Fomrn-«r-Rih, four seams are very distinctly 
marked ; but that which usual indicates the line 
of transition between the Globigerina limestone 
