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 other 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 



