John H. Cooke—Flint and Chert in Maltese Limestone. 159 
“nodules having more or less symmetrically shaped outlines. In 
composition they also vary greatly, the larger masses being composed 
of flint (silex), while the smaller nodular forms consist of chert 
(phtanite), which is an impure calcareous variety of flint. 
At Fommer Rih and along the hill-slopes already referred to, the 
differential degradation to which the nodular masses and their matrices 
have been subjected has resulted in the complete isolation of the 
former, and they have thus been caused to project from the faces of 
the cliffs and escarpments as bold conical bosses. 
In none of the nodules are these exposed portions entire, as all of 
them have been more or less acted upon by the same meteoric 
agencies that have removed the limestone from around them. 
In many instances the disintegration has proceeded by the peeling 
off of laminated scales, while in others small shapeless masses have 
broken away and left the weathered surfaces irregularly prismatic 
in character. 
Viewed with the naked eye both the nodules and the larger 
masses are exceedingly homogeneous; but when examined under a 
low magnifying power, sections of foraminifera, small molluses, and 
other organisms are to be seen embedded. 
In none of the specimens that 1 have examined have I observed 
any of the fish-scales to which Spratt alluded in his brochure ; but 
I cannot venture to say that, therefore, such remains are either 
absent or of rare occurrence. 
In colour both the flint and the chert vary widely, graduating 
through all the intermediate shades of grey, fawn, blue, and black. 
The interiors of the nodules are generally of a jet black colour, 
a fact which is probably due to the presence of carbonaceous 
matter, as much of it disappeared when subjected to the action of 
the blow-pipe flame. This black interior often graduates into a 
semi-translucent grey towards the outer edges, thus causing the 
concretions when cut transversely to present the appearance of 
being made up of a series of concentric layers of varying hues; such 
specimens are not, however, so common as are the uniformly black, 
grey, and fawn coloured varieties. 
The limestone surrounding the masses and the nodules is invariably 
changed into chert more or less pure in character. This cherty lime- 
stone is often of a colour similar to that of the enclosed nodule, 
and unless carefully examined it is often difficult to say where the 
line of demarcation between the two lies. 
The former, however, is neither so compact nor does it present, 
when broken by means of a smart blow with a hammer, the con- 
choidal fracture which is so characteristic of the latter. 
From the similarity which exists between the characters of these 
flints and cherts and those which occur so plentifully in other lime- 
stone formations, it seems probable that the origins of both are to 
be traced to analogous causes. 
The Maltese varieties are found only in the most highly 
calcareous portions of the strata, embedded among the Globigerine 
of which the greater part of the formation is made up. 
