SOUTHERN AFRICA. 181 
Travelling along the feet of the Rietberg before mentioned, 
and on its northern side, we passed several fine clumps of 
forest-trees in the kloofs of the mountain, and among these 
obtained three new species of timber which were not observed 
in the woods near Zwart Kop's bay. The face of the coun- 
try was here particularly nigged ; the hills were composed of 
sand-stone, resting on bases of blue slate. In the perpendi- 
cular side of one of these hills was oozing out a salt of various 
colors, similar to that described and found near the salt lake 
of Zwart Kop's river. The upper part of the face of this hill 
consisted of large, regular, rhomboidal tablets of stone, whose 
projecting angles formed a kind of cornice to the face : these 
rested on a mass of purple slate, crumbling into dust. The 
white veins of quartz that appeared to have once been liquid, 
and to have flowed through the slate in curved seams, were 
now far advanced in their transitions into clay ; pieces of 
these veins were friable between the fingers ; several prismatic 
quartz crystals were found in a corroded state, and evidently 
decomposing into the same earth. The change of quartz in- 
to clay is indeed perceptible in all the mountains of Southern 
Africa. It should seem that this is the last stage of all the 
earthy bodies. Future discoveries in chemistry may perhaps 
demonstrate that the earths, now considered as having dif- 
ferent bases, were originally formed of one, and are reducible 
to the same, ultimate principle ; or that they are convertible 
substances. That by exposure to, and combination with, 
the different airs which float in the atmosphere, or with water 
impregnated by different materials, they become subject to 
pass into the nature of each other. 
