ROCK SPECIMENS FROM THE ISLAND OF SOCOTRA. 
275 
nearly the whole length of the island, is for miles covered with dunes of blown sand. 
On the north these plains occur chiefly at the mouths of the streams, and are the sites 
of the only places which may be called towns. 
“The internal hilly part of the island may be roughly and shortly described as a 
wide undulating and intersected limestone plateau of an altitude averaging 1,000 feet, 
which flanks on the west, south, and east a nucleus of granitic peaks approaching 
4,000 fbet high. The whole of this hilly region is deeply cut into by ravines and 
valleys. These in the rainy season are occupied by roaring torrents, but the majority 
of them remain empty during the dry season. There are, however, many perennial 
streams on the island, especially in the central granitic region, where amongst the hills 
the most charming bubbling streams, dashing over boulders in a series of cascades or 
purling gently over a pebbly shingle, make it hard to believe that one is in such 
proximity to the desert region of Arabia. Few of the perennial streams reach the 
shore in the dry season—most of them are fiumaras. 
“ The eastern end of the island is most destitute of water. Here in the dry season 
are no rivers, and, springs being rare, it is the most arid region, 
“ Igneous, metamorphic, and sedimentary rocks compose the island. The funda- 
mental rock is granitic. This crops out, as I have mentioned, towards the middle of 
the island, forming a series of bare pinnacles and crags, projecting, with singularly 
fantastic look, from the plateau below. This rock also shows on the slopes of the 
valleys and ravines below the compact limestone which caps it and forms the surface 
rock of the hill plateaux. This limestone attains in places, as seen on the cliff faces, a 
thickness of two or three hundred feet. Superficially, over wide areas it is rotted and 
broken into a jagged surface, over which progression is by no means easy, while at 
other spots it forms broad, smooth slabs. A shaly rock and coarse-textured purple 
sandstone, in beds dipping at all angles, crop out in the valleys and on the shore, 
whilst forming the shore-plains and the bases of the valleys is a recent breccia and 
conglomerate. Cutting through all these rocks, and altering them to a considerable 
extent, occur dykes and extensive masses of doleritic rocks and felstones, which vary 
much in texture.” 
Professor Balfour landed on the shore of Gubbet Gollonsir at the north-western 
extremity of the island and explored the district fringing this bay for some distance 
inland, so as to examine the high ground on either side of the level valley which opens 
out to the sea. The uplands here consist of a thick deposit of limestone, probably of 
middle tertiary age, but in many cases remarkably compact and hard, so that it has at 
times considerable resemblance to the well-known dolomites of the Italian Tyrol. This 
mass of limestone rests unconformably upon a group of highly crystalline gneisses, asso¬ 
ciated with diorites and perhaps with hornblende schists, which in general character 
correspond with the Hebridean series in the north-west of Scotland. These older rocks 
are frequently exposed in the beds of valleys and in the lower part of the walls of the 
plateau. The same description applies to the elevated districts traversed by Professor 
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