840 A VOLCANIC ERUPTION IN EAST AFRICA 
even milked their own breasts to appease the anger of the 
spirits believed to reside within the mountain. 
The lava has flowed for a long distance down the valleys 
which score the flanks of the mountain, and, in cooling, it has 
cracked into irregular masses, having the appearance of cakes 
of grey cement. 
Farther from the mountain, the country is covered with a 
powdery ash, and this extends, mixed with soda, to a distance 
of twenty-five to thirty miles ; and large areas of grazing-land 
have been temporarily destroyed. In some places the deposit 
of ash resembles black sand. 
The western flanks of Gelei Mountain, which rises to a 
height of nearly 10,000 feet on the east side of Lake Natron, 
were covered with ash and soda, and the water-holes on the 
mountain were so fouled with soda that they have become 
unusable ; the springs on the east and south-east side were, 
however, unaffected. 
The river, known as Engare Sero, or Mito miwile, rising in 
the high land to the west of Donyo L’Engai, is unaffected, but 
its banks are covered with a thick deposit of volcanic ejecta. 
The water in both areas of this stream is still sweet, because 
the springs rise high up in the western plateau. 
Heavy rain occurred in this region early in June 1917, 
and it is recorded that for a period of four to five days the rain- 
water was strongly alkaline and undrinkable by cattle. The 
Masai state that many herds of cattle, located in places where 
the only water was in pools, have died through drinking the 
alkaline water. 
The mountain is now quiescent and only slightly smoking. 
The ejection of vast quantities of soda from this volcano appears 
to be evidence that sodium carbonate is one of the principal 
constituents of the magma from which the eruptions of the 
Rift Valley are derived. The persistence of soda in so many of 
the lakes in that valley, from Rudolf down to Natron and 
Eyassi, is a marvellous phenomenon. 
Mr. Parkinson quotes in one of his papers a theory of Gautin 
to explain the genesis of thermal waters. 
It is assumed that the subterranean magma is largely 
composed of sodium silicate, and that plutonic water charged 
