ROCK SPECIMENS FROM THE ISLAND OF SOCOTRA. 
291 
abundant foraminifers in these rocks, ranges from the miocene upwards, hence it is 
probable that the age of these Socotra limestones is miocene. 
Conclusion. 
From the above remarks it would appear that in Socotra we have, as the foundation 
stones and “ core ” of the island, if the phrase be permissible, a mass of rock of very 
great antiquity. There is clear evidence of the presence of gneissic rocks which in 
their lithological characters resemble closely those which exist in the north-west of 
Scotland, the Malvern Hills and one or two other localities in our own island, in 
Northern America, and in many other parts of the globe. By whatever name these 
may be called, and however they may be correlated one with another, it is evident 
that their antiquity is enormously great, and that they had attained their present 
mineral condition before the earliest palaeozoic rocks were deposited. Associated with 
these are granites, which, though of later date, are probably also of great antiquity. 
In the Sinai peninsula we have also gneiss, schists, and various granitic rocks. Of the 
latter I possess a small collection, given to me by Professor E. H. Palmer,* and the 
resemblance of some of the specimens to Those of Socotra is very remarkable. In the 
geological notes added by the Rev. F. W. Holland to the Repjort of the Ordnance 
Survey (ch. viii.) we find it stated, indeed, that the prevailing rock, in the Sinai region, 
is syenite (by which term probably hornblendic granite is meant), so that out of several 
hundred specimens he only possessed two or three of true granite. This may be, but 
my specimens from the summits of Serbal, of Jebel Musa, and Um Shomer closely 
resemble some of the Socotra rocks, especially the first and second, which are coarse 
reddish granites composed almost wholly of quartz and felspar (pegmatites). From 
the summit of Serbal also comes a finer grained granite, and I have an ordinary granite 
from Wady Sigillia. Other specimens, exactly as in the Socotra collection, might be 
either true igneous or highly met amorphic rock. In the Sinai region the old gneiss 
appears only to have been recognised in the northern part, where it forms an irregular 
trough to the north of Jebel Serbal, the higher peaks (like the Haggier range in 
Socotra) being granite. I miss, however, from the Socotra district, or find but feebly 
represented—for there is one specimen which may belong to it—the friable variably - 
| coloured sandstones which form so marked a feature in some parts of the Sinaitic 
peninsula ( e.g ., Wady Mokatteb)t. These, after having been assigned to more than 
one geological epoch, were referred by Mr. Holland, on the evidence of fossils, to the 
* He was a member of the Sinai Survey Expedition in 1868-9. Two months after this paper was 
read, he was murdered by Arabs. The circumstances of his death are well known, but I may be allowed 
to pay a passing tribute to the memory of a singularly accomplished and learned man and very valued 
friend. 
t This absence of the sandstone is probably an accident (the rock being very friable), for Professor 
Balfour mentions “purple sandstones ” (see p. 275). 
2 p 2 
