But it would be tedious to recount further the divisive ways of these arch-deceivers, and I shall only refer to another mimetic form, which for cool Pharisaism takes the palm from every creeping or flying thing. I first saw this menteur à triple ètaye on the Tanganyika plateau. I had lain for a whole week without stirring from one spot—a boulder in the dried-up bed of a stream, for this is the only way to find out what really goes on in nature. A canopy of leaves arched overhead, the home of many birds, and the granite boulders of the dry stream-bed, and all along the banks, were marked with their white droppings. One day I was startled to see one of these droppings move. It was a mere white splash upon the stone, and when I approached I saw I must be mistaken; the thing was impossible; and now it was perfectly motionless. But I certainly saw it move, so I bent down and touched it. It was an animal. Of course it was as dead as a stone the moment I touched it, but one soon knows these impostures, and I gave it a minute or two to become alive—hastily sketching it meantime in case it should vanish through the stone, for in that land of wonders one really never knows what will happen next. Here was a bird-dropping suddenly become alive and moving over a rock; and now it was a bird-dropping again; and yet, like Galileo, I protest that it moved. It would not come to, and I almost feared I might be mistaken after all, so I turned it over on its other side. Now should any sceptic persist that this was a bird-dropping I leave him to account for a bird-dropping with six legs, a head, and a segmented body. Righting the creature, which showed no sign of life through all this ordeal, I withdrew a few paces and watched developments. It lay motionless on the stone, no legs, no head, no feelers, nothing to be seen but a flat patch of white—just such a patch as you could make on the stone in a second with a piece of chalk. Presently it stirred, and the spot slowly sidled across the boulder until I caught the impostor and imprisoned him for my cabinet. I saw in all about a dozen of these insects after this. They are about half the size of a fourpenny-piece, slightly more oval than round, and as white as a snowflake. This whiteness is due to a number of little tufts of delicate down growing out from minute protuberances all over the back. It is a fringe of similar tufts round the side that gives the irregular margin so suggestive of a splash; and the under surface of the body has no protection at all. The limbs are mere threads, and the motion of the insect is slow and monotonous, with frequent pauses to impress surrounding nature with its moribund condition. Now, unless this insect with this color and habit were protectively colored it simply would not have a chance to exist. It lies fearlessly exposed on the bare stones during the brightest hours of the tropical day, a time when almost every other animal is skulking out of sight. Lying upon all the stones round about are the genuine droppings of birds; and when one sees the two together it is difficult to say whether one is most struck with the originality of the idea, or the extraordinary audacity with which the rôle is carried out.*
* It is a considerable responsibility to be the sole witness to this comedy—though I saw it repeated a dozen times subsequently—but, fortunately for my veracity, I have since learned from Mr. Kirby of the British Museum that, there is an English beetle, the Cionus Blattaria, the larval form of which "operates" in a precisely similar way.
It will be apparent from these brief notes that mimicry is not merely an occasional or exceptional phenomenon, but an integral part of the economy of nature. It is not a chance relation between a few objects, but a system so widely authorized that probably the whole animal kingdom is more or less involved in it; a system, moreover, which, in the hands of natural selection, must ever increase in intricacy and beauty. It may also be taken for granted that a scheme so widespread and so successful is based upon some sound utilitarian principle. That principle, I should say, was probably its economy. Nature does everything as simply as possible, and with the least expenditure of material. Now consider the enormous saving of muscle and nerve, of instinct and energy, secured by making an animal's lease of life to depend on passivity rather than activity. Instead of having to run away, the creature has simply to keep still; instead of having to fight, it has but to hide. No armor is needed, no powerful muscle, no expanse of wing. A few daubs of color, a little modelling of thorax and abdomen, a deft turn of antennæ and limb, and the thing is done.
At the first revelation of all these smart hypocrisies one is inclined to brand the whole system as cowardly and false. And, however much the creatures impress you by their cleverness, you never quite get over the feeling that there is something underhand about it; something questionable and morally unsound. The evolutionist, also, is apt to charge mimetic species in general with neglecting the harmonious development of their physical framework, and by a cheap and ignoble subterfuge evading the appointed struggle for life. But is it so? Are the æsthetic elements in nature so far below the mechanical? Are color and form, quietness and rest, so much less important than the specialization of single function or excellence in the arts of war? Is it nothing that, while in some animals the disguises tend to become more and more perfect, the faculties for penetrating them, in other animals, must continually increase in subtlety and power? And, after all, if the least must be said, is it not better to be a live dog than a dead lion?
VIII.
A GEOLOGICAL SKETCH.
From the work of the various explorers who have penetrated Africa, it is now certain that the interior of that Continent is occupied by a vast plateau from 4000 to 5000 feet above the level of the sea. In five separate regions—in the North-east, in Abyssinia, in the Masai country, on the Tanganyika plateau, and in the district inland from Benguela—this plateau attains a height of considerably over 5000 feet; while towards the coast, throughout their entire length, both east and west, it falls with great uniformity to a lower plateau, with an elevation of from 1000 to 2000 feet. This lower plateau is succeeded, also with much uniformity along both coast lines, by littoral and deltoid plains, with an average breadth from the sea of about 150 miles.
The section which I am about to describe, entering Africa at the Zambesi and penetrating inwards to the Tanganyika plateau, traverses each of these regions in turn—the coast-belt, the lower fringing table-land, the great general plateau of the country, and the third or highest elevation of the Tanganyika table-land. To deal thoroughly with so vast a region in the course of a single exploration is out of the question; and I only indicate here a few of the rough results of what was no more than a brief and hasty reconnaissance.
The first and only geological feature to break the monotony of mangrove-swamp and low grass plain of the coast-belt is the debris of an ancient coral-reef, studded with sponges and other organisms. This reef is exposed on the Qua-qua River, a little above Mogurrumba, and about fifty miles from the sea. It is of small extent, at no great height above the present sea-level, and, taken alone, can only argue for a very inconsiderable elevation of the coast region. Some twenty miles farther inland, and still only a few yards above sea-level, an inconspicuous elevation appears, consisting of sedimentary rocks. This belt is traceable for some distance, both north and south, and a poor section may be found in the Zambesi River, a few miles above the grave of Mrs. Livingstone at Shupanga. The rocks in question, which are only visible when the Zambesi is very low, consist of a few thin beds of red and yellow sandstones, with intercalated marly sandstones and fine conglomerates. Sedimentary rocks, in somewhat similar relation, are found at least as far north as Mombassa, above Zanzibar, and as far south as the Cape; and it seems probable that the whole of the plateau of the interior is fringed by this narrow belt. No organic remains have been found in this series north of Natal, but the fossils of the Cape beds may shed some light on its horizon. Associated probably with these rocks are the great beds of coal which are known to exist some distance up the river in the neighborhood of Tette.
A short distance above the junction of the River Shiré with the Zambesi the first hills of the plateau begin almost abruptly. They occur in irregular isolated masses, mostly of the saddle-back order, and varying in height from 100 or 200 to 2000 feet. Those I examined consisted entirely of a very white quartzite—the only quartzite, I may say, I ever saw in East Central Africa. At the foot of the most prominent of those hills—that of Morumballa—a hot-spring bubbles up, which Livingstone has already described in his "Zambesi." Hot-springs are not uncommon in other parts of the Continent, and several are to be found on the shores of Lake Nyassa. These are all of the simplest type, and although the temperature is high they leave no deposit anywhere to indicate their chemical character.