Vol. 59.] HOCKS FROM SOUTHERN ABYSSINIA. 297 



exhibiting rather micropegmatitic inclusions, and one interesting 

 crystal of augite. It is large (^ inch long), irregular at the edge as 

 if corroded, and encloses numerous clear, small grains of augite like 

 a micropegmatite, in the arrangement of which a slight orientation 

 along what may be cleavage-planes can be traced. The explanation 

 is difficult, but, although local melting and recrystallization seem 

 possible, it is perhaps more likely that, after the small augites had 

 formed, the large crystal developed around them, spreading until 

 solidification of the neighbouring groundma6S prevented further 

 growth and produced an irregular outline. 



In a dark slaty-grey basalt from Chellahah the groundmass 

 contains a little glass, and microlithic felspars exhibiting a fluxional 

 arrangement. The rock from a hill near Mendi is compact, sub- 

 ophitic, but with small amygdales. 



(Hi) Glassy basalts include a pebble from a brook towards 

 Errer, one specimen from near Hirna (although this might be a 

 basic andesite), others from the hill east of Laga-Hardim Camp 

 (including one or two from the upper series), from Eantalli, from 

 the surface between Akaki and Addis Abbeba, and from Gatama. 

 These rocks are mostly blackish, compact or finely glittering. The 

 siena-brown glass contains imperfect skeleton-crystals and granules 

 of opacite which render the matrix confusedly dusky. It encloses 

 greenish palagonitic patches and some small crystals. Two or three 

 specimens are purplish, and some vesicular, others containing por- 

 phyritic crystals. 



(iv) Vesicular or scoriaceous rocks (doubtless basalts). — 

 The most scoriaceous are from the talus near Addi Adeya, the 

 greatest number from the hill east of the camp at Laga Hardini, 

 many from the upper series of rocks. Two others are from near 

 the Hawash River, two from Eantalli, and one from Toki. 



(2) Phonolites and Allied Rocks. 



Hocks containing nepheline occur at two localities. 1 They are 

 found at Garsa, about long. 42° E., beyond Lake Haramaia in 

 the South-East of Abyssinia, with sandstones and grits, and near 

 Bilo (about long. 37° E.), much farther west on the Gibbe River, 

 connected with the extensive area of Southern Abyssinia which is 

 occupied almost wholly by volcanic rocks. The Saquala rocks, from 

 south of Addis Abbeba, are probably allied to the phonolites. 



Two specimens of a blackish, almost glassy-looking rock from 

 Bilo (or near that place), weathered brown, contain large (j-inch) 

 cleaved glassy crystals. These sometimes are singly twinned, with 

 two cleavages at about right angles, sparsely cracked, extinguish 

 straight, have low double refraction, and probably are sanidine ; 

 although a possible twinning like that of anorthoclase is very faintly 



1 Compare also A. Rosiwal, ' Beitr. geol. Kennt. des ostl. Afr.' pt. ii, Denkschr, 

 k. Akad. Wissensch. Wien, vol. lviii (1891) p. 465 ; J. W. Gregory, Quart. 

 Journ. GeoL Soc. vol. lvi (1900) p. 205 ; & G. T. Prior, Min. Mag. vol. xii 

 1 1900) p. 255. 



Q. J. G. S. IS T o. 234. x 



