e, although sterile and desert, are
remarkable for the number and great bulk of the indigenous quadrupeds.
We there meet with an elephant, five species of rhinoceros, a
hippopotamus, a giraffe, the bos caffer, the elan, two zebras, the
quagga, two gnus, and several antelopes. Nor must we suppose, that while
the species are numerous, the individuals of each kind are few. Dr.
Andrew Smith saw, in one day's march, in lat. 24 degrees S., without
wandering to any great distance on either side, about 150 rhinoceroses,
with several herds of giraffes, and his party had killed, on the
previous night, eight hippopotamuses. Yet the country which they
inhabited was thinly covered with grass and bushes about four feet high,
and still more thinly with mimosa-trees, so that the wagons of the
travellers were not prevented from proceeding in a nearly direct
line."[146]

In order to explain how so many animals can find support in this region,
it is suggested that the underwood, of which their food chiefly
consists, may contain much nutriment in a small bulk, and also that the
vegetation has a rapid growth; for no sooner is a part consumed than its
place, says Dr. Smith, is supplied by a fresh stock. Nevertheless, after
making every allowance for this successive production and consumption,
it is clear, from the facts above cited, that the quantity of food
required by the larger herbivora is much less than we have usually
imagined. Mr. Darwin conceives that the amount of vegetation supported
at any one time by Great Britain may exceed, in a ten-fold ratio, the
quantity existing on an equal area in the interior parts of Southern
Africa.[147] It is remarked, moreover, in illustration of the small
connection discoverable between abundance of food and the magnitude of
indigenous mammalia, that while in the desert part of Southern Africa
there are so many huge animals; in Brazil, where the splendor and
exuberance of the vegetation are unrivalled, there is not a single wild
quadruped of large size.[148]

It would doubtless be impossible for herds of mammoths and rhinoceroses
to subsist, at present, throughout the year, even in the southern part
of Siberia, covered as it is with snow during winter; but there is no
difficulty in supposing a vegetation capable of nourishing these great
quadrupeds to have once flourished between the latitudes 40 degrees and
60 degrees N.

Dr. Fleming has hinted, that "the kind of food which the existing
species