valve, and bivalve.

In every salt-pan in the country there is a spring of water on one side.
I can remember no exception to this rule. The water of these springs is
brackish, and contains the nitrate of soda. In one instance there are
two springs, and one more saltish than the other. If this supply came
from beds of rock salt the water would not be drinkable, as it generally
is, and in some instances, where the salt contained in the pan in which
these springs appear has been removed by human agency, no fresh deposit
occurs. It is therefore probable that these deposits of salt are the
remains of the very slightly brackish lakes of antiquity, large portions
of which must have been dried out in the general desiccation. We see an
instance in Lake Ngami, which, when low, becomes brackish, and this view
seems supported by the fact that the largest quantities of salt have
been found in the deepest hollows or lowest valleys, which have no
outlet or outgoing gorge; and a fountain, about thirty miles south of
the Bamangwato--the temperature of which is upward of 100 Deg.--while
strongly impregnated with pure salt, being on a flat part of the
country, is accompanied by no deposit.

When these deposits occur in a flat tufaceous country like the present,
a large space is devoid of vegetation, on account of the nitrates
dissolving the tufa, and keeping it in a state unfavorable to the growth
of plants.

We found a great number of wells in this tufa. A place called
Matlomagan-yana, or the "Links", is quite a chain of these never-failing
springs. As they occasionally become full in seasons when no rain
falls, and resemble somewhat in this respect the rivers we have already
mentioned, it is probable they receive some water by percolation from
the river system in the country beyond. Among these links we found many
families of Bushmen; and, unlike those on the plains of the Kalahari,
who are generally of short stature and light yellow color, these were
tall, strapping fellows, of dark complexion. Heat alone does not produce
blackness of skin, but heat with moisture seems to insure the deepest
hue.

One of these Bushmen, named Shobo, consented to be our guide over the
waste between these springs and the country of Sebituane. Shobo gave us
no hope of water in less than a month. Providentially, however, we came
sooner than we expected to some supplies of rain-water in a chain of
pools. It is impossible to convey an idea of the dreary sc