Vol. 59.] ROCKS FROM SOUTHERN ABYSSINIA. 301 



contains small porphyritic crystals (felspar, hornblende) and included 

 fragments of rock like small rounded lapilli. Although these 

 specimens appear to be fluxional andesites, they might possibly 

 represent some of the phonolitic series. 



Of two porphyrites obtained near Bilo, one, a rich red compact 

 rock with porphyritic crystals of felspar, has a very fine-grained 

 microlithic grouudmass, coloured by iron-oxide. The secoud, from 

 the hill towards Abbra Gibbe, is rather felsitic in aspect, aud the 

 groundmass is found to consist of narrow felspar-crystals with 

 fluidal orientation. A purplish-grey porphyrite, somewhat similar, 

 comes from east of Garsa Camp. 



Several andesites occur in the hill east of Laga-Hardim Camp, in 

 the lower series of rocks. A slice from one of these contains 

 patches (probably due to flow-brecciation) in which a roughly- 

 reticulate arrangement is rather like that in some nepheline-rocks, 

 where segirine is grouped to form the lines of the network. 1 



The other andesites from this locality often enclose small 

 scoriaceous fragments and porphyritic crystals, sometimes broken 

 or worn. They generally exhibit a fluxional structure, and one of 

 them, from near the Hawash Eiver, is traversed by platy jointing ; 

 another, from the Fantalli Hills, is dark, even blackish in the hand- 

 specimen. 



Some pale-brown rocks from Chaffi Dunsa contain many angular 

 fragments of crystals and of rocks, felsite or porphyrite. The 

 groundmass consists of wavy patches rich in secondary kaolin, and 

 of streaks of brown glass, so the rock is probably a flow-brecciated 

 andesite, and not a tuff. Several andesites from near Addis Abbeba 

 (the southern end) resemble those from near Laga Hardim. 



Trachytes (?). — Two rocks at the back of the Eesidency at Addis 

 Abbeba are vesicular, yellow to brick-red in colour. One of them 

 exhibiting marked fluidal structure includes green microliths and 

 incipient crystals generally squarish in section, suggestive of a potash- 

 felspar, as if the rock might belong to the sanidine-trachytes. The 

 glassy groundmass of two specimens contains fragments doubtless 

 caught up in flowing. A specimen from Laga Hardim is compact, 

 and of a dull olive-green. The colourless glassy base is crowded with 

 minute granular epidote and pyroxene (?), and the fragments enclosed 

 are of felsite, felspar, and glassy basalt. A rather earthy-looking 

 greenish rock from the Fantalli Hills exhibits flow-structure, and 

 contains a few fragments. 



CI a y stones. — Several claystones, probably decomposed andesites 

 or trachytes, occurred at Addis Abbeba and at the Akaki Gorge. 



Obsidian. — A small flake of black obsidian, apparently artificially 

 chipped, was found not far from Jigjiga (with a flake of chert and 

 some quartz) near the place where Mr. H. W. Seton Karr obtained 

 Palaeolithic implements. 2 



1 Compare that in the Saquala rock, p. 300. 



2 Journ. Anthropol. Inst. vol. xxv (1896) p. 271. 



