842 A VOLCANIC ERUPTION IN EAST AFRICA 
with C0 2 breaks up the sodium silicate into amorphous silica 
and sodium carbonate. This would of course satisfactorily 
explain the existence of the ridges of flint-like silica which 
occur on the flats near Magadi Lake. 
It may be, however, that the magma contains vast amounts 
of metallic sodium, and that the oxidation of this has provided 
the motive power for the vast eruptions which have taken 
place in this area. However, be that as it may, there now 
appears to be little doubt that the soda is what may be termed 
inter-telluric, and is not produced by the decomposition of 
soda felspars or other rocks containing the alkali in question. 
There is no record of any previous eruption of this mountain, 
but it was always remarkable for large white patches on the 
sides of its cone and a pinnacle on its summit — the latter was, 
however, blown away during the recent eruption. Herr Kasin, 
a German scientist, who accompanied Dr. M. Scholler’s expedi- 
tion, informed me that he had ascended Donyo L’Engai and 
found that the white deposit on the upper portion of the cone 
was soda. The slopes are now covered with a grey whitish 
deposit, which is said to give the impression of snow that has 
fallen on a rough surface. 
An examination of the German geological map discloses 
the fact that, south of Lake Natron, the Rift Valley continues 
to run southwards through Lake Mweri and Dalanga ; another 
branch runs south-west through Lake Eyassi, and in between 
the two there is a fault valley which the Germans named the 
Hohenlohe Graben. From the direction of the two latter, it 
may be surmised that the complicated scheme of faulting, which 
caused them, originated in the vicinity of the volcano Donyo 
L’Engai. This junction has, however, been masked by an 
extraordinary number of large volcanoes commencing at the 
north end of Eyassi and running in a north-east direction : 
these are Oldiani, Ngorongo, Ololmoti, Ololmasin, Elanairobi, 
Kerimassi, and finally, Donyo L’Engai. 
Whether this terrific amount of volcanic action produced 
the split in the Rift, or vice versa, it is impossible at present to 
conjecture ; but it is safe to say that there must have been, and 
probably still exist, very severe stresses in the earth’s crust in 
this region. 
