302 miss c. a. raisin on [May 1903, 



Pumiceous tuffs. — These are fine-grained, dusty or sandy- 

 looking rocks. Three are from east of Laga Hardim from the lower 

 series, two from the Akaki Gorge, and two from near Bilo. In all, 

 the powdered material consists almost wholly of colourless glass- 

 chips, generally vesicular and pumiceons, with felspathic material 

 in one specimen. 



IV. Sedimentary Rocks. 



(a) Arenaceous Rocks. 



Sandstones and sands occurred between the coast and the 

 Abyssinian frontier, and in the south-eastern part of that country. 

 One greyish-banded quartzite, with spots coloured by haematite, 

 collected east of Garsa, resembles rocks of a rather early geological 



Quartzose sandstones similar to those of late Mesozoic age 

 include one from Dobeia, not far from the coast, many at and near 

 Jigjiga Pass, and between that frontier-pass and Chercher. In the 

 last-named area, most of the ferruginous sandstones and grits (so 

 characteristic of many African collections) were obtained. In all, 

 the quartz-grains often interlock, forming almost a quartzite, and 

 the secondary zone along their edge is in one rock partly opaline 

 silica. In another, lines curved like perlitic structure, or crossing 

 at right-angles, may have been caused by heat from neighbouring 

 volcanic masses. 



The action of blown sand is sometimes exhibited, as in a loose 

 fragment from above Hargaisa, found by Lord Lovat. This speci- 

 men of a banded, slightly calcareous sandstone is bluntly conical, 

 but rounded, and is worn into ridges along the alternating bands. 



The compact ferruginous sandstones (almost quartzites) are 

 purple or reddish-brown, with white felspar-speckling, banded, and 

 often exhibit current-bedding. Infiltrating water has sometimes 

 formed an ' iron-pan ' or concretions, which in one of the coarser 

 grits occur as rounded nodules with concentric structure. 



One fine-grained red rock from near Lake Chercher, might be a 

 rotten tuff, but is possibly only a clay. 



(b) Calcareous Rocks (and Organic Rocks). 



Crystalline limestone. — Two fragments of a white, coarse 

 crystalline limestone ' from among granite . . . between Errer and 

 Harrar ' contain flakes, three-tenths of an inch long, of a bright- 

 brown pleochroic phlogopite. 



Dolomites. — South-west of Berbera, a whitish subcrystalline 

 dolomite occurs at a distance of about 15 miles, and a minutely 

 granular dolomite at about 24 miles. The latter, a ' vein in a 

 granitoid rock,' contains angular fragments of quartz, plagioclase, 

 green hornblende, and limestone, and a few obscure organisms. 

 Other granular dolomites, from near the Jigjiga Pass and Eyambiro, 

 consisting of minute rhombohedra, exhibit inclusions like those in 



