The speed at which these little beasts can travel is little short of marvellous. The fastest runner would not have the remotest chance of catching them; when frightened, they will go off at a pace that the natives say even a horse cannot equal. The steady rate which the one whose tracks I had followed had kept up for so many miles, shows that they can travel long distances without tiring, and that they not only can, but do.
It is in this marvellous capacity for getting over the ground, and their habit of hoarding up provisions, that the explanation of their ability to live in these districts can, I believe, be found.
Absolutely barren as this district seems to be, there are here and there patches of grass, quite dead to all appearances, but which have probably shed their seed on the surrounding ground. Even in these arid districts rain is not unknown—there were stories in Dakhla of a regular downpour that was said to have occurred not many years before, when rain fell in such quantities that many of the mud-built houses of the oasis melted before it and fell down. Rainfall such as this, or even a heavy shower, might cause the seed to sprout. The grass is usually found growing on the stiffest clay, which would hold the moisture from the rain for a considerable time, and, aided by the great heat of the warmer months, cause the grass to grow with extreme rapidity. Upon this grass and its seeds these rats could easily live, and from it they could store up in their underground burrows provisions to last them for a very long time. Rats are known to be able to subsist on hard grain alone, that does not contain more than ten or fifteen per cent of moisture.[18] They are probably acquainted with a number of places where these grasses grow, and, as it is known that they never drink, by making a store near each, and travelling from one to another as their depots become exhausted, they can maintain themselves for several years of drought. The tracks that we saw running continuously for nine miles at a stretch, with hardly a break, may have been those of a rat travelling from one of his storehouses to another. A journey such as this could hardly have been undertaken without some definite object in view. A fifty mile run would be nothing to one of these little creatures, so they would be able to draw their supplies from thousands of square miles of country, within which, even in this arid desert, they would be able to find plenty to live upon. In one place, too, we found green terfa bushes, from which they may perhaps have obtained some nourishment, and possibly sufficient moisture from the green portions of the plants to enable them to exist without drinking—though an occasional journey of a hundred miles or so, into an oasis to procure water, would be quite within the locomotive powers of these extraordinary little creatures.
APPENDIX I
THE GEOGRAPHY AND WINDS OF THE LIBYAN DESERT
THE views on the geography of the Libyan Desert, current at the time of my visit to the country, are summarised by Mr. F. R. Cana in the valuable paper and map that he contributed to the “Geographical Journal.”[19] Writing of this desert he says: “Some knowledge of its character has been obtained where it borders the Nile, and to the north along the edge of the Cyrenaican plateau . . . the general character of the desert is that of rocky wastes in the north and east, and a vast sea of sand in the centre.”
The rocky wastes begin on the north, immediately to the south of the cultivable belt along the North Egyptian coast; the desert here rising to form a plateau. This tableland is succeeded by a vast depression, portions of which lie below sea-level. This hollow runs from Siwa Oasis in an easterly direction towards the Nile. Reference will be made to this huge valley later on.
The southern side of this depression has never, I believe, been mapped, but, beyond it, the level of the desert rises again to a limestone-capped plateau, that in places is over a thousand feet above sea-level. The western limit of this has not, I believe, been ascertained in its northern part, but towards the east it is bounded by the Valley of the Nile, where it forms the towering cliff on its western side that is familiar to all visitors to Egypt. About the latitude of Qena the plateau narrows down to a width of about a hundred miles, its western limit being the great escarpment that bounds the oasis of Kharga on its eastern side.
The geography of this limestone tableland, and of the desert beyond it up to the Egyptian-Tripolitan frontier, was tolerably well known at the time of my arrival in Egypt; but, with the exception of Kufara and the other oases in the same group, practically the whole desert beyond it was a terra incognita, the domain of the Senussi, and, as stated in Mr. F. R. Cana’s paper, considered to consist of an impassable sea of enormous sand dunes.