NATURALIST 
207 
THE MEDITERRANEAN 
fa. Limestone 2 % to 
» IV - Glob - Limestone-, h 10 % to 
l 18 %. 
„ V. Lower Cor. Limestone, traces 
In the Greensands and the Globigerina Lime- 
stone, the highest percentages were found in the 
black or chocolate coloured nodules that were 
interspersed through the beds. These nodules 
occur very irregularly and in but small quantities 
in the former, so that, from a commercial point of 
view, the formation needs no further consideration. 
In the latter, they are found in great abundance, 
occuring in well defined layers that are both 
uniform in their thickness and unvariable in 
their distribution. As it is, therefore, with the 
Globigerina rock that we shall have to deal, a 
few details relative to its principal characteristics 
will be necessary before proceeding to consider 
the phosphate beds that lie interstratified with it. 
This formation, as the section (fig. 1.) shows, 
extends throughout the length and breadth of 
both islands, but in the north-western and western 
parts, it is overlain by the Clays, Greensands, 
and Upper Coralline Limestone which effectually 
mask it over a considerable district, but its out- 
crops along the valleys and in the eastern parts of 
Malta extend over an area that is equal to about 
two-thirds of the total extent of the island. 
Between the Great Fault and Marsa Scirocco, 
an area of about 50 square miles has been planed 
down to such an extent as to remove from it a 
capping of deposits that had an average thickness 
of 350 feet. The surface contour of this district 
is therefore very irregular, and as the Globigerina 
itself has in many cases been also subjected to 
considerable erosion, the upper phosphate seams 
contained in it have been left exposed as the 
surface layer. 
In Gozo the denudation of this formation has 
not been so extensive, and therefore it exhibits a 
more uniform thickness in that island than it does 
in Malta, and appears as the surface deposit over 
au area equal to about one fifth of the total area 
of the island, the greater part of which is found 
in the bottom of the valleys, and at the bases of 
the hills. 
Proceeding now to consider the various divi- 
sions of the formation we find that they consist of 
at least four varieties of rock each of which varies 
considerably in its lithological characters, and 
interstratified with which is a series of seams of 
phosphatic nodules which is very regular in its 
distribution. 
The following shows the order in which these 
beds and their intercalated layers of phosphate 
rock occur. 
In Gozo and in the western half of Malta the 
whole series crops out along every valley and hill 
side, but where the Globigerina rock itself serves 
as the surface deposit the intermediate layers of 
limestone often mask the nodule beds in such a 
manner as to completely hide from view all evi- 
dence of their presence. Where this occurs the 
soil is usually very poor and unproductive. 
The first nodule seam is variable in its nature 
and thickness in different localities. For example 
in the southern coast exposures it does not ave- 
rage more than 9 inches in thickness, and the 
nodules are sparsely distributed; but in the cliff 
sections in the centre of the island, it has an 
average thickness of 1 foot 3 inches and the 
nodules are numerous and compact. 
Formation 
Subdivisions 
Thickness 
a. A greyish, fine-grained freestone 
1.5 to 20 ft. 
- 
h. First seam of phosphatic nodules 
1 ft. 
c. A white, compact, fine grained free-stone 
40 to 50 ft. 
Globigerina Limestone 
d. Second nodule seam 
•2 ft. 
e. Irregular bands of nodules sparsely distributed 
variable. 
/. A soft bluish limestone 
50 ft. 
g. A white limestone with chert nodules 
100 feet. 
h. Fourth nodule seam. 
3 to 4 ft. 
