The Pedras Negras of Pungo Andongo in Angola -^t^ 



Pedras Negras, I shall now proceed to the description of the 

 phenomenon which causes their black appearance at certain times 

 of the year. On my arrival at Pungo Andongo at the end of 

 October (the spring season in the southern hemisphere), the 

 colossal rocks, projecting high above their girth of vegetation had 

 a pretty equal aspect of grey or greyish yellow colour, shaded 

 darker in a few places near the top. From this I was inclined to 

 concur in the opinion that the black colouring, so much spoken 

 of, probably resulted from an optical delusion. This idea became 

 more confirmed after I had ascended the higher mountains several 

 times. On the flat part of their summits I noticed pools over- 

 grown with Nymphese and Aponogeton ; but neither in the ponds 

 (stagnant deep waters of small extent) nor on their borders could 

 I trace any kind of vegetation which might possibly account for 

 the colouring of the rocks. However, very soon afterwards, I was 

 convinced to the contrary. During the following month, several 

 successive thunder storms brought down heavy rains. In the 

 following December I observed in several places on the chfifs 

 facing the Presidium perfect black stripes pointing downwards, 

 their dark colour in conspicuous contrast with the general 

 aspect of the other stone masses. These stripes increased 

 considerably in breadth and length in the course of a few 

 days, and other new ones appeared on rocks previously of grey 

 yellow colour. Now was the time to investigate the extra- 

 ordinary phenomenon ; and with the view of tracing its origin, 

 I ascended on the next bright morning the Pedra Songue (pro- 

 nounced Songhe) known under this name among the natives 

 as one of the highest mountains in the Presidium. Arrived on its 

 plateau, I found that the continuous rain-fall had swelled all the 

 ponds to excess, and filled every hollow with water. On the brink 

 of these waters, mostly covered with sterile mosses, my attention 

 was immediately attracted by a shiny black substance which ex- 

 tended in all directions, with few interruptions, towards the descend- 

 ing edge of the cliffs. There I saw its further course along the 

 streamlets made by the overflowing of the ponds. Examining 

 this black substance with the aid of a strong pocket-lens, I saw 

 at once that it was a filamentous Alga ; and from that moment 

 the riddle of the Pedras Negras was solved. On the follow- 

 ing day I subjected specimens of the Alga to a minute careful 

 microscopical examination, and its characteristics proved it 

 to be probably a non-described species of the prolific genus 



TRAVEL. c 



