ROCK SPECIMENS FROM THE ISLAND OF SOCOTRA. 
287 
ground mass, and more or less of a spherulic structure. The second is a particular 
interesting example, longish microliths of ferrite-stained felspar being scattered, or 
irregularly grouped, among clear quartz and occasionally formed into true spherulites, 
which are often enclosed by a dark ring. The microliths frequently indicate by their 
grouping an incipient micrograpliic structure (Plate 7, fig. 4). [4408] and [4413] 
are rhyolites showing a very marked fluiclal structure, the former affording one of the 
best examples of “ flow brecciation ” that I have ever seen; fragments of lava, often 
differing considerably in their minor characteristics, being entangled in the matrix of 
the slide, showing that the partially solidified rock from time to time has been broken 
up and swept along by the pressure of the still liquid mass behind (Plate 7, fig. 5). 
The rock has been subsequently cracked and the fissures cemented by infiltrated 
minerals, among which is opal. The locality of the last two rocks is indicated as “ close 
to Azorah (almost half way between the north and south coasts).” [4446] and [4448] 
are rocks of a dull purple colour, with small amygdaloids (Plate 7, fig. 6). The matrix 
consists of very minute elongated felspar microliths in a base, rendered almost opaque with 
ferrite and opacite; opal, chalcedony, and a clear mineral resembling felspar occupying the 
vesicles of the rock. Its relations are perhaps rather with the andesites than the true 
trachytes. [4431], from nearer Kittim, where it is associated with conglomerates and 
forms low hills, looking in places much like a lava flow, differs from the others in 
colour, being a compact pale grey rock like some of those which I have obtained from 
Moneadhmore Glen, in Arran, or even from North Wales; it has a rather variable 
cryptocrystalline base, ferrite-stained, in which are scattered many small felspar crystals 
(probably orthoclase), quartz, and a chloritic mineral. Apart from the confirmatory 
evidence given by Professor Balfour, I should have felt no hesitation in asserting 
that some, at least, of these rocks formed parts of lava flows; they are anterior in 
date to the limestone beneath which they pass. 
From the hill of Afero, which, Professor Balfour states, reminded him of a volcanic 
neck, west-south-west of Azorah, approaching the eastern end of the Haggier range, 
come more reddish compact quartz-felsites and rhyolites of the usual type. A specimen 
[4436] which has been examined microscopically exhibits a fluiclal structure, in parts 
1 cryptocrystalline, in parts rather microcrystalline, and much ferrite-stained ; but it is 
needless to dwell on points of only varietal interest. 
The last specimens from this group of rocks examined microscopically were collected 
m situ near Feraighey, on the southern side of the Haggier range. [4440] is a very 
compact pale Indian-red felsite, resembling a group described above [4458, &c.], but is 
a little more spherulitic. [4420] is nearer to [4446] in general character; there are 
some curious rounded concretionary spots of opacite, and perhaps one or two minute 
amygdaloids. 
Mica-traps. 
From Socotra we have one or two representatives of this outlying and rather vague 
but convenient group. One [4270] is from a dyke forming the floor of a gully on the 
