506 Miss C. A. Raisin— Rocks from Socotra. 
Carlsbad twinning with simultaneous extinction, they appear to 
be mostly orthoclase. These felspars, and some larger crystals of 
a pale green hornblende, occasionally twinned, exhibit a certain 
orientation, which is practically the only indication of a fluidal 
structure seen under the microscope. 
Other Igneous Rocks.—In the diorites, kaolinized felspar, and 
hornblende mostly in good preservation, are closely intercrystallized, 
with some appearance of an ophitic structure. One compact black 
rock occurs, which seems to be of a basaltic character. Another 
fragment, evidently from a lava-flow, may be a basalt, in which the 
augite is less clearly individualized, or it may, perhaps, be better 
classed with the andesites. It contains vesicles, filled up mainly 
with calcite, but with some chlorite; it has other calcite apparently 
pseudomorphic, and a zeolitic mineral seems also present. A fairly 
large cluster of calcite scalenohedra has been sent, and appears to 
have been formed in or ona greenish felsite, very decomposed fragments 
of which are found adhering. There is one specimen of a compact 
black rock, which is rather puzzling, even under the microscope ; 
although it might be a very fine-grained igneous rock of rather basic 
character, yet it seems most probable that it consists of fine ashy 
material, with much fragmental felspar in good preservation. 
Sedimentary Rocks. (1). Argillite—This is a green flinty rock, 
with a marked and even banding. It is composed of fine material, 
and contains small angular fragments with a torn look, many of 
which are plagioclase. Except that the banding here is more evenly 
marked, probably in consequence of a pressure, which has acted 
across the lamination, this rock is very similar to those described by 
Prof. Bonney. It clearly bears out his suggestion, that the argillites 
of Socotra are probably not due to local contact metamorphism, but 
may represent some part of an old sedimentary series. 
(2). Grits.—In a grit, which appears to consist mainly of frag- 
mental felspar of more than one kind, there seems to have been 
a secondary deposition, probably of silica, which has remained as a 
cavernous skeleton, where the original grains have weathered out. 
Another specimen is composed, almost exclusively, of two of the 
constituents of a granitic rock—quartz and felspar—and is thus 
not unlike the Torridon sandstone of the Scotch Highlands. 
(3). One specimen of a reddened limestone is very full of frag- 
ments of Gasteropod and Lamellibranch shells, the calcite of which 
exhibits rhombohedral cleavage, and is of a deep red colour, appa- 
rently iron-stained. 
xcept for a few structural characteristics, these rocks are mainly 
interesting as being an independent collection, which, although 
small, agrees closely with the description already given of Socotra 
rocks. ‘The grit, here noticed, may be possibly of recent consolida- 
tion, or may belong to the sandstones, which Prof. Bonney mentions 
as probably present. The groups which he describes will include all 
the other specimens, except the fossiliferous limestone, although this 
might belong to the formation of the foraminiferal rock.’ ‘The 
_} If the limestone belongs to some other series, it might possibly be a representa-— 
tive of Dr. Rochebrune’s Neocomians of Ouarsanguélis land. 
