Vol. 59.] ROCKS FROM SOUTHERN ABYSSINIA. 303 



the ' vein ' described above, but chiefly of quartz. One of three 

 specimens from south of Laga-Hardim Camp exhibits oolitic grains 

 within a subcrystalline matrix. Two • chalky-looking rocks,' one 

 not far from Addi Adeya with volcanic rocks, the other near 

 Jummat ' with granite,' may be similar rock decomposed ; and a 

 friable specimen, effervescing briskly, and consisting of minute 

 rhombohedra of calcite, is probably a decomposed limestone. 



Brecciated or concretionary limestones. — In one 

 brecciated-looking limestone a pale brownish matrix contains 

 darker brown, imperfectly-rounded fragments. A marked black 

 rim gives them a likeness to pebbles, and rounded quartz-grains or 

 pebbles are similarly embedded. Some resemblance, however, to 

 tufaceous or concretionary limestone suggests the action of infil- 

 trating water. The black margin of the fragments is undoubtedly 

 due to secondary deposition, since it extends along wavy planes in the 

 rock and along joints or cracks. Five typical specimens have been 

 brought, all from between Berbera and the Abyssinian frontier. 

 One from the rock forming the hill at Dobeia, exhibits a weathered 

 surface, coarsely grooved and pitted (? by sand-blast), and encloses 

 small fragments of quartz and of dolomite. Of two rocks from the 

 camp at Jefa Medr, one contains larger fragments (i to j inch), the 

 other exhibits wavy lines and narrow veins like those of septaria. 

 In a compact rock ' protruding from the surface at many points ' 

 towards Jigjiga, are fragments of stony limestone. The margin 

 of these is marked by concentric streaks or lines, which consist of 

 limonite and veins of dolomite. The cracking or jointing of these 

 limestones (along curving or rectangular lines) may be possibly due 

 to heating by the sun's rays. Subsequently infiltration occurred, 

 and secondary deposition generally of iron-oxide or of dolomite. 



A compact limestone from the hill at Jefa Medr has apparently 

 undergone subsequent brecciation, and may be possibly related to 

 the above. 



Limestones with organisms. — Some of the foraminiferal 

 limestones ' about 15 miles south-west of Berbera, forming the 

 main mass of the hill,' are compact, pinkish with whitish patches, 

 and much dolomitized. They contain the alga LithotJtamnion 

 well preserved, and Amphistegina (2 ). A second type is hard, com- 

 pact, whitish or drab-coloured, often breaking with subconchoidal 

 fracture (resembling some described in 1888 also from Somaliland ] ). 

 Near Jigjiga Pass this rock contains Globigerina, chambered Rotaline 

 foraminifera, Textularia, Orbulina, and Lagena. To the south of 

 Laga Hardim a similar rock exhibits Miliola and Tesctularia. 

 Several specimens from Burka to Hirna include cylindrical branching 

 structures (| inch across) difficult to determine, and in the micro- 

 scopic slice one or two specimens of a Dactylopora (?). The sections 

 of the larger structures suggested some resemblance to a sponge ; 

 and Dr. G. J. Hinde most kindly undertook a careful examination of 



1 ' £>n some Kock-Specimens from Somaliland ' Gecl. Mag. 1888, pp. 417, 

 418. 



