ROOK SPECIMENS FROM THE ISLAND OF SOCOTRA. 
28 L 
possible that among them may have been some of metamorphic origin referable to the 
Archaean series, for, as my experience in Cornwall and Scotland has shown me, it is 
sometimes by no means easy to distinguish the one from the other in hand specimens. 
Dolerites, basalts, dc. 
The information furnished to me does not allow me to attempt any classification of 
this group. Some of the basalts cut the limestones and so are among the most modern 
known igneous rocks of the island, but whether all these augitic rocks are of the 
same date it is impossible to say : probably they are not. 
A dolerite from the plain on the south-west of the stream in Gollonsir Valley [4051], 
is a rather coarsely crystalline rock, consisting mainly of whitish felspar and black augite. 
The former, under the microscope, proves to be well preserved labradorite, the crystals 
of which have fairly regular linear boundaries, and in form are rather broad oblongs. 
The augite, which has solidified after the felspar, is full, in one or two cases, of irregular 
grains of opacite, which sometimes make up almost the whole of the crystal. Incipient 
conversion into uralite is exhibited, crystals of augite having sometimes an irregular 
border of the latter mineral; while sometimes minute scales of it are disseminated in the 
nearly colourless augite crystal. In one or two instances almost the whole crystal is 
replaced by uralite. 
One of the dykes near Kadhab village [4198], I leave, after microscopic examination, 
with some hesitation among the basalts. It retains some traces of a clear glassy base 
crowded with opacite and other microliths, some acicular and colourless, which with 
some larger crystals are rather like anorthite, others are of a greenish-yellow colour, 
fibrous or filmy ; these being generally associated in irregular patches, with interspersed 
specks of opacite. They are most like replacements of an augitic constituent. A little 
hornblende can also be recognised. There are some indications of fluiclal structure, 
and the rock evidently approaches the augite-andesite group. 
[4454], one of a group of rocks of doleritic aspect, from the base of Azalin on the 
bank of the Hasainho, speckled whitish and blackish, consists of (a) labradorite in well 
defined crystals, evidently the first mineral to consolidate; (b) a slightly brown, rather 
dichroic augite, which in one case approaches diallage in its close cleavage; (c) a dark 
brown hornblende, sometimes inclining at the edges to sap-green (Plate 7, fig. 1). 
This paragenesis—for I think the whole aspect of the hornblende forbids the idea that 
it is of secondary formation (the uralites being generally green, and often quite pale)— 
though not very common is far from being unprecedented. It seems, for example, 
rather frequently in the old diabases of North Wales, and in the gabbro of Mont Colon 
(Pennine Alps). [4449], one of a very similar group of specimens, from the “rocks of 
which Azalin is composed,” consists of well crystallized labradorite in good preservation, 
olivine, sometimes partially replaced by serpentinous microliths, opacite, augite, with a 
little diallage and hornblende. Some of the last mineral is certainly of secondary 
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