Miss C. A. Raisin—Rocks from Somali Land. 415 
Over sheltered valleys, such as the Koton, there is spread a thick 
covering of rich soil. The main valleys are long, and have a gentle 
slope; and in these, large boulders rarely occur, but they are 
common in the short and steep ramifications, and the exposed slopes 
of the hills show signs of very extensive denudation. The detritus, 
thence derived, has been carried down, until its transport was 
checked by the sea and by the fringe of coral reefs, and the deposit 
then accumulated backwards, bnilding up the immense alluvial 
plain in the form of a long, narrow, and scarcely perceptible basin, 
parallel to the coast-line. The light, argillaceous portion of the 
detritus reached the coast first. It was there rapidly deposited and 
formed an impermeable stratum, which retains both the local rain 
water and that which is absorbed further inland. As a result, 
abundance of water is obtainable all along the coast, from the Gulf 
of Tajurra to Bulhar, within three or four feet of the surface, while 
in the alluvial plain further inland the wells have to be sunk to a 
considerable depth. One of the circumstances, which tend to 
maintain the water supply in the coast basin is that the rainy 
seasons above and below the Ghats do not coincide. In illustration 
of this, Capt. King mentions that he saw the Taknota river, when in 
a state of flood, discolouring the sea to a distance of more than a 
mile, although no rain had fallen near the coast for some months. 
The specimens collected by Capt. King have been examined, and 
slides for the microscope prepared from the most interesting. 
Igneous Rocks. (1.) Porphyrite.—This rock, of a dingy-brown, 
containing porphyritic felspars, chiefly plagioclase, and other crystals 
possibly pseudomorphs after pyroxene, gives good illustration of the 
replacement of felspar. Granular epidote has developed, generally 
from the heart of the crystal, and forms pale-green patches, well 
marked even in the hand specimen. In one felspar, there is a fan- 
shaped group of chlorite; apatite crystals are also present, one of 
which seems to have been corroded by intruding portions of the 
ground-mass. 
(2.) Hornblende-Diabase-—The crowded crystals of large green 
hornblende are very dichroic, giving high tints with crossed Nicols 
(purples and reds), but they pass by a gradual transition to lighter- 
coloured less dichroic patches within, and thus recall the more 
abrupt variation from brown to green hornblende in the Little Knott 
rock.’ It would seem that a secondary change has attacked the 
mineral, but has not completely spread over the interior. There is 
a tendency to an orientation in the hornblende cleavages, and the 
crushed and schistose structure of the rock may well be the result of 
pressure, which has acted on what was possibly once a gabbro. 
(3.) Granite.—This granite, whose locality is not given, may perhaps 
have occurred in association with the metamorphic rocks of the 
valleys, and may contribute to the fragmental quartz, which is said 
to be so abundant there. The felspar is chiefly microcline; and, 
included both in it and in the quartz, is a dark green metallic-looking 
mica, so small in amount that the rock is almost a binary granite. 
1 Q.J.G.S. 1885, vol, xli, p. 512, pl. xvi. fig, 2. 
