154 
In the Heart of Africa 
eruptive canal I discovered two further flues running down 
vertically into the earth, which like the main one, had burst 
out from the encircling terraces (not from the crater-floor proper) 
and were smoking faintly.” 
During the whole of his sojourn at Namlagira Kirschstein 
kept a regular record of the meteorological conditions ; made 
scientific investigations into the relations of the parasitic craters; 
determined their exact shape and position, and carried out a 
great many further tasks. These dealt chiefly with the manifold 
volcanic phenomena encountered in the comparatively recent lava 
field piled south of Namlagira. Besides characteristic volcanic 
cinder chimneys, “ hornitos ” as they are called, and the singular 
lava cloaks on charred tree trunks, there was a long lava tunnel 
(155 metres), very typical in feature, and in many respects in¬ 
structive, which particularly arrested our attention. As is well 
known, lava tunnels of this description are formed by the stream 
of lava cooling off very quickly on the surface whilst the fiery 
stream continues to flow on beneath the congealed outer crust, 
leaving the latter finally in the shape of a hollow tube, often a 
kilometre in length. In the one we investigated (see illustra¬ 
tion) the end part of the tunnel was quite intact and merged 
into an open cavern. Further on, however, the tunnel had caved 
in so that it formed a lava fissure running in a direct line from 
north-west to south-east, four metres in width and seventeen 
metres in depth. It may be questioned whether a large pro¬ 
portion of the gaping lava rifts found in otheir volcanic regions, 
and which are attributed to tectonic action, may not have arisen 
in the same way. 
There was another interesting result of Kirschstein’s investi¬ 
gations in the Namlagira district. He was successful in dis¬ 
covering a series of those most primitive forms of manifesta¬ 
tions of volcanic forces which Branca first described with any 
accuracy as occurring in the neighbourhood of Urach in Swabia, 
and introduced to science under the apposite title of “volcanic 
embryos.” These are steep-walled eruptive canals, sometimes 
only a metre in breadth, which have been blown up through the 
