LUMBWA CAVES 
481 
The thickness of the deposit in this cave was greater than 
some of the others, and reached a maximum of about seven 
feet thick. The usual lava beds occur above the rock, whilst 
below is a rhyolite, sometimes amygdaloidal. Occasional 
dykes of harder rock traversed the cave, and pillars of rock 
had been left at intervals as roof-supports. The roof was 
sound, and rock-falls appeared to be rare. The natives w T ork 
in the cave by the light of bundles of twigs, which give off 
comparatively little smoke. 
This was the biggest cave visited, and appeared to he the 
one most worked. The field tests did not, however, give such 
good results of phosphate as some of the others. The digging 
is done by means of rude iron picks — the pick blade being set 
in a wooden club (see Pig. 1). 
The quarried material is transported to the mouth of the 
cave in small wooden troughs of light wood, which are slid 
along the ground (see Pig. 2). 
Fig. 2.- — Wooden trough used for convey- 
ance of salt earth in caves, Lumbwa. 
All the work inside the cave is done by men. Streams of 
women carry away the rock in wicker creels, carried on the 
