64 
TRAVELS IN 
have attended to the ifthmus that now unites them, the more T 
am perfuaded that, inftead of its having, in latter ages, been 
covered with the fea, the time is yet to come when that event 
will take place. I have already obferved, that the furface is 
from twenty to thirty feet above the level of high water mark; 
that the fand upon it, except vs^here it is drifted into ridges, is 
feldom three feet deep, and it refts upon fandftone or hard 
gravel. I can now add, that ridges of blue fchiftus and granite 
rocks appear on various parts of the furface fo elevated. Ad- 
mitting that the fandftone and the gravel, which is fcarcely pof- 
fible, were the fragments of the mountains by which this plain 
is enclofed on two fides, yet neither the fchiftus nor the granite 
could have been adventitious ; thefe two materials muft have 
been primeval, and they abound on the moft elevated as well 
as on the lower parts of the ifthmus ; in fituations that cannot 
be lefs than one hundred feet above the level of the fea. But 
if the fea has retreated one hundred feet, in its perpendicular 
height, the whole continent of Africa muft have been an ifland 
at the time that the Cape promontory was an ifland. What 
changes may have taken place with regard to the canals and the 
inland parts of the ifthmus of Suez in the courfe of two or 
three thoufand years it is not neceflary to inquire, but the 
ifthmus of Suez, fo long ago, was a flat fandy ifthmus, not 
much higher, nor lower, in all probability, than at the prefent 
day. 
I fhall now offer my reafons for fuppofing the fea to be gain- 
ing upon the land in Southern Africa. The plain that fkirts the 
Lion's Rump, and is waftied by Table Bay and the fea, ufually 
3 called 
