Journal of Traz'el and Natural History 



THE PEDRAS NEGRAS OF PUNGO ANDONGO 

 IN ANGOLA. 



By Dr Friederich Welwitsch. 



'T^HE "Black Rocks of Pungo Andongo," designated in 

 ''■ most of the antient writings as " the Presidium of the 

 Pedras negras" are situated in the interior of Angola, about 

 1 80 geographical miles eastward from the Atlantic coast. 

 They are mentioned in the books of missionaries and other 

 travellers, upwards of two centuries ago, as a great wonder of 

 nature, and have claimed the attention of all travellers who have 

 since visited them. Of these observers none, not even the sagacious 

 Livingstone, has paid any attention to the surprising change of 

 colour to which the above named rock-mountains are subject every 

 year, and which led to the denomination of the place, and even of 

 the whole district. A prolonged residence in Pungo Andongo, 

 where I passed several months, commissioned by the Portuguese 

 Government to study the vegetation and capabilities of the soil for 

 future agricultural purposes, gave me a favourable opportunity of 

 observing the entire progress of their coloration, convincing me 

 that the intense blackness of the rocks, conspicuously seen at 

 certain periods of the year, is not produced, as supposed, by their 

 disintegration nor by the refraction of light, but by the growth 

 and wonderfully quick propagation of a small cryptogamous 

 plant during the annual rainy season, which at first marks wth 

 dark stripes the rocks in various places, then gradually entirely 

 overgrows them, and gives them the appearance of being covered 

 by a black mantle. 



As every phenomenon in nature is more easily understood if 

 compared with similar, or, at least, analagous, appearances already 

 known elsewhere, I shall ask the reader to allow me to draw his 

 attention for a few minutes away from the interior of Africa to 

 other parts of the world, where we shall find that the variegated 

 colouring of larger tracts of land and water frequently arises from 

 the wide spread growth of excessively small cryptogamic plants, 

 often only to be observed with the aid of a microscope. 



This is not a rare occurrence in nature. Even in the streets of 

 our European towns we see, during rainy springs, the more shaded 



