5 
290 PROFESSOR T. G. BONNET ON A COLLECTION OF 
foraminifera abound. Among these we can recognise* Globigerina (abundant) 
Rotalince —probably two forms of Planorbulina, one like Ammonoides, and the other 
outspread like Mediterranensis—Textulctria (more than one form), Amphistegina, and 
possibly a small Nummulites, with fragments of mollusca, polyzoa (?), and of other 
organisms which I cannot recognise. The matrix is rather earthy. 
A specimen [4048] from the cliff capping the ridge above Hainjou (west end of the 
island) is a very compact pale cream-coloured limestone. Microscopic examination 
shows a matrix of dusky grey material, with minutely-crystallized calcite and probably 
a little dolomite, which occurs also in thin veins, and some minute granules which may 
be glauconite. It contains several Rotalince, possibly Planorbulina and Discorbina, 
and perhaps Rotcdia, together with a large fragment rather resembling a piece of 
a Cristellaria. 
Buff limestones from the Kadhab Plain, [4188] and [4195]. The former contains 
numerous mineral fragments, apparently quartz and felspar, with organisms broken 
and whole, among which Amphistegina and Miliola are recognisable, and bits of the 
shells of mollusca. The organisms are more or less dolomitized. The latter contains 
many Globigerince with Amphistegina (small), perhaps an Orbitoides, and fragments of 
mollusca and polyzoa. This rock also is slightly dolomitized. 
A specimen of limestone [4107] from the plateau west of Ras Mom, near the 
eastern extremity of Socotra, is a buff-coloured rock with a minute oolitic structure, 
the weathered surface being full of small holes. Under the microscope we found a 
clear dolomitic matrix full of darkish rings, circular to irregular oval in form, with a 
radial-fibrous structure, and as a nucleus commonly either a fragment of quartz or of 
a foraminifer, though sometimes they inclose simply the matrix; sometimes also the 
concentric structure ex tends'to the centre of the oolitic grain. 
[4456]—a very compact pale buff limestone from the top of Ras Mom, in appearance 
almost exactly like a bit of Schlern or Dachstein dolomite, is shown on microscopic 
examination to be a true dolomite. It contains numerous organisms, which, as is 
commonly the case, are more completely dolomitized than the matrix, and so rendered 
rather difficult of identification. There are many foraminifera, among them certainly 
Amphistegina , and perhaps Nummulites, Globigerina, with fragments which I believe 
to be polyzoa. 
As regards the geologic age of these limestones, Globegerina has had a long exis¬ 
tence, like Textularia ; Nummulites began long since, and still lingers, but was most 
abundant in the eocene time ; Orbitoides began in cretaceous and disappeared before 
the latest part of the tertiary age ; Amphistegina, however, which is one of the most 
* As I have not worked much at thin sections of foraminiferal limestone, I submitted all these slides 
to Professor Rupert Jones, F.R.S. With his wonted kindness, though at the time far from well, he 
examined them and gave me a series of notes, which are embodied in the text, so that the identifications 
rest upon his authority, than which it would be difficult to find a better. 
