SOUTHERN AFRICA. 329 
brown ochraceous ftone (the oxyd of iron combined with clay) 
liejuft below the furface, where they are fometimes found in 
extenfive ftrata. In fuch fituations they have the beft grapes 
and the beft of every fort of fruit, which may be owing, pro- 
bably, to the manganefe that this kind of dark brown iron- 
ftone generally contains, and which modern difcoveries in che- 
miftry have afcertained to be particularly favourable to the 
growth of plants. 
There is neither a volcano nor a volcanic produft in the 
fouthern extremity of Africa, at leaft in any of thofe parts 
where I have been, nor any fubftances that feem to have un- 
dergone the adion of fire, except malTes of iron-ftone found ge- 
nerally among the boggy earth in the neighbourhood of fome 
of the hot fprings, and which appear like the fcorise of furnaces. 
Pieces of pumice- ftone have been picked up on the fhore of 
Robben Ifland, and on the coaft near Algoa Bay, which muft 
have been wafted thither by the waves, as the whole bafis of 
this ifland is a hard and compa6l blue fchiftus, with veins of 
quartz running through it, and of the eaftern coaft iron-ftone 
and granite. 
The climate of the Cape may be confidered as not unfriendly 
to vegetation ; but by reafon of its fituation, within the influ- 
ence of a kind of Monfoon or periodical winds, the rains are 
very unequal, defcending in torrents during the cold feafon, 
whilft fcarcely a fliower falls to refrefli the earth in the hot 
fummer months, when the dry fouth-eaft winds prevail. Thefe 
winds blaft the foliage, bloflbm, and fruit of all thofe trees that 
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