SOUTHERN AFRICA. 
227 
bafes of blue flate. In the perpendicular fide of one of thefe 
was oozing out a fait of various colors, fimilar to that defcribed 
and "found near the fait lake of Zwart Kop's river. The upper 
part of the face of this hill confifted of large, regular, rhomboi- 
dal tablets, whofe proje£ling angles formed a kind of cornice 
to the face : thefe refted on a mafs of purple flate, crumbling 
into duft. The white veins of quartz that appeared to have 
once been liquid, and to have flowed through the flate in cur- 
ved feams, were now far advanced in their tranfitions into 
clay ; pieces of thefe veins were friable between the fingers ; 
feveral prifmatic quartz chryflials were found in a corroded 
fl:ate, and evidently decompofing into the fame earth. The 
changes of quartz into clay are perceptible in all the mountains 
of Southern Africa. It fhould feem that this is the lafl: fl:age 
of all the earthy bodies. Future difcoveries in chemiftiry may 
perhaps demonfl:rate that the earths, now confidered as having 
different bafes, were originally formed of one, and are reducible 
to the fame ultimate principle ; or that they are convertible 
fubftances. That expofure to, and combination with, the dif- 
ferent airs that float in the atmofphere, or with water impreg- 
nated by different materials, they become fubjed: to pafs into 
the nature of each other. 
Several detached pieces of hematite were found among the 
mafs of flate. Indeed there is fcarcely a mountain in Africa 
that does not produce iron ores ; and ochres are every where 
found in the greateft abundance. The finefl; of thefe are met 
with in the ftate of impalpable powders inclofed in cruftaceous 
coverings of a reddifii color, of the hardnefs and confiflence of 
G G 2 baked 
