OiRIGrHsr-A-I-. -A-IRTIOHilES. 



* 



I. — Non-German Sources of Potash. 

 By Arthur Holmes, D.Sc, A.R.C.S., F.G.S. 



Abyssinian Deposits. — During 1911 an Italian resident in Eritrea 

 discovered a remarkable occurrence of potash salts in the Piano del 

 Sale, near the provisional boundary between the Italian colony and 

 Abyssinia. On account of its equivocal situation, development was 

 somewhat handicapped during the early stages by Abyssinian 

 hostility. Fortunately these preliminary difficulties were successfully 

 overcome, and the deposit proved to be of great assistance to the 

 Allied Powers during the war. The rate of production has gradually 

 increased, and the estimated output for 1918 is stated to be 

 equivalent to 50,000 tons of KC1. 



The situation of the deposit is indicated on the accompanying 

 geological sketch-map by a black rectangle (due south of the Bay of 

 Haoachil, and just touching the recently determined boundary) 

 which marks the position of Mt. Dellol. The Piano del Sale, or 

 "Plain of Salt", is a depressed region almost entirely below sea- 

 level. It is, in fact, as indicated on the map by a dotted line, 1 

 approximately bounded by the contour of sea-level. The depression 

 is separated from the Red Sea, of which it is structurally a part, by 

 the lavas and sediments of the Aden Series. On the west the edge 

 of the Abyssinian plateau, carved in an ancient complex of meta- 

 morphic and igneous rocks, constitutes the real western boundary of 

 the Red Sea Rift, and forms one side of the funnel-shaped sunkland 

 into which the East African Rift Valley opens out near Ankober. 

 The Piano del Sale is itself the exposed basin-like surface of a gigantic 

 saline deposit, in which the older beds are disposed around the 

 periphery, while the younger beds outcrop at successively lower 

 levels towards the interior. Beds consisting mainly of gypsum, and 

 representing the earliest phase of deposition, outcrop conspicuously 

 around the northern and eastern sides, and similar beds also appear 

 on the western edge, opposite Mt. Dellol. Within the gypsum zone, 

 and at a lower level, though resting upon it, is a wide expanse of 

 rock-salt over 20 miles across, and generally free from alluvium. 

 The level gradually drops until it reaches about 390 feet below sea- 

 level around Mt. Dellol. This so-called "mount" is a rectangular 

 mass consisting mainly of rock-salt, the summit of which is within 

 a foot or two of sea-level. It has been weathered into curious 

 castellated forms, so that when seen from a distance in the slanting 

 rays of the sun it resembles a vast mediaeval fortress. 



At the south-eastern corner of this curious edifice, in the heart of 

 the depression, red and yellow masses of sylvite are exposed at the 



1 For a map showing the relation of this area to the Red Sea and to the 

 Rift Valley of East Africa, see G. Dainelli & O. Marinelli in Atlanta d' Africa, 

 by A. Ghisleri, 1909, p. 139, fig. 6. The information from which the 

 geological sketch-map was compiled was mainly obtained from this publication 

 (see pis. xxxi, xxxii, and pp. 133-9). 



