the Island, &c._ By John Charles Melliss, F.G.S., &c. London: 1875.

[120] Mr. Marsh in his interesting work entitled _The Earth as Modified by
Human Action_ (p. 51), thus remarks on the effect of browsing quadrupeds in
destroying and checking woody vegetation.--"I am convinced that forests
would soon cover many parts of the Arabian and African deserts if man and
domestic animals, especially the goat and the camel, were banished from
them. The hard palate and tongue, and strong teeth and jaws of this latter
quadruped enable him to break off and masticate tough and thorny branches
as large as the finger. He is particularly fond of the smaller twigs,
leaves, and seed-pods of the _Sont_ and other acacias, which, like the
American robinia, thrive well on dry and sandy soils, and he spares no tree
the branches of which are within his reach, except, if I remember right,
the tamarisk that produces manna. Young trees sprout plentifully around the
springs and along the winter water-courses of the desert, and these are
just the halting stations of the caravans and their routes of travel. In
the shade of these trees annual grasses and perennial shrubs shoot up, but
are mown down by the hungry cattle of the Bedouin as fast as they grow. A
few years of undisturbed vegetation would suffice to cover such points with
groves, and these would gradually extend themselves over soils where now
scarcely any green thing but the bitter colocynth and the poisonous
foxglove is ever seen."

[121] _Coleoptera Sanctae Helenae_, 1877; _Testacea Atlantica_, 1878.

[122] On Petermann's map of Africa, in _Stieler's Hand-Atlas_ (1879), the
Island of Ascension is shown as seated on a much larger and shallower
submarine bank than St. Helena. The 1,000 fathom line round Ascension
encloses an oval space 170 miles long by 70 wide, and even the 300 fathom
line, one over 60 miles long; and it is therefore probable that a much
larger island once occupied this site. Now Ascension is nearly equidistant
between St. Helena and Liberia, and such an island might have served as an
intermediate station through which many of the immigrants to St. Helena
passed. As the distances are hardly greater than in the case of the Azores,
this removes whatever difficulty may have been felt of the possibility of
_any_ organisms reaching so remote an island. The present island of
Ascension is probably only the summit of a huge volcanic mass, and any
remnant of the original fauna a