waters, set in at the close of the Pliocene period, and gave us our wide-spread "drifts," with their glaciated stones and their thick irregular beds of clay and sand. The later epochs of the Post-Pliocene pass into historic times, and the whole period corresponds with the existence of man upon the earth.

The opening of Cainozoic times showed at once the predominance of mammals. The humble creatures of the Mesozoic era now assumed an immense superiority and variety. Like the Permian and Triassic reptiles, they were adapted to a great range of food and habits, and some became specialised as vegetable-feeders, some as flesheaters; some took to the sea, in the form of great toothed whales, while others, as little bats, flew in the air. The reptiles with equal rapidity became narrowed down to their present restricted types; their empire had been utterly taken from them.

The older Cainozoic mammals were, however, widely different from any that we possess at the present day, and often combined the characters of two or more living genera. The humbler forms of life, however, such as the molluscs, closely resembled our modern types, and lamellibranchs and gastropods were in Eocene times already largely in excess of brachiopods. The ammonites, so essentially characteristic of the Mesozoic periods, had entirely disappeared, though their ancient ally, Nautilus, still existed. The plant-life also approximated to that of our own times, and honey-sucking insects are consequently found as fossils in Cainozoic strata.

The wonderful mammalian deposits of Provence and Greece,1 and of the Siwálik Hills in India, show us how, even in Pliocene times, the highest forms of life were still strangely distinct from those of the Post - Pliocene and Recent period. The types that we now know were then represented by more gigantic forms, which waged war upon one another, until Man appeared among them. Here they met a creature capable of killing off the fiercest of them by superior art and cunning, and of leading the more docile into perpetual and even hereditary slavery. The exact period of Man's entry upon the earth may never become precisely known. The wonderful skull styled Pithecanthropus, found in Java by Dr. Dubois 2 in 1891, associated with ex

1 For a charming account of Cainozoic mammals, see Gaudry, "Les Ancêtres de nos animaux."

2 Trans. R. Dublin Soc., vol. vi. (1896), p. 1; and Nature, vol. lii. p. 115.

tinct Pliocene mammals, and the chipped flint-flakes recorded by Dr. Noetling from Burma, which are said to underlie 4620 feet of Pliocene strata, give us some idea of the oldest epoch at which we may expect to find remains of man.1

In any case, the base of the Pliocene is comparatively near us, while the commencement of the Paleozoic era lies some forty times as far behind us. Estimates may be made, from the thickness of the marine strata composing the successive systems, as to the relative time that elapsed during their accumulation. To convert these data into actual years seems beyond our present powers, though several calculations have been made, based upon the rate of accumulation near existing shores. Giving the Cainozoic era its fullest. value, as displayed to us by the Italian deposits, we may allow it to have been slightly longer than the Mesozoic era; while the Paleozoic era was four times as long as the Mesozoic. If we start our annals at the base of the Cambrian, with a time-point which we will call o, and divide a column representing subsequent time into 100 divisions, like the degrees on a thermometer, then we arrive at the following approximate results (fig. 24).

(i) The Paleozoic era extended from o to 64 degrees of our scale.

(ii) The Mesozoic era terminated at 80 degrees.

(iii) The Cainozoic era extended over the remaining 20 degrees, including the present time.

(iv) In this comparatively short time of 20 degrees, as we shall see for ourselves when we come to our final observations (Chapter X.), the most extraordinary changes went on in the surface-features of the globe, side by side with marked changes in the forms of mammalian life.

66

(v) The oldest remains of man are found at 99 degrees of our time-scale, or one unit only from its summit; while human history," in the ordinary sense, even that of the Chaldæans and the Chinese, can only be represented by a minute fraction of a degree.

Here we are met, then, by the most remarkable and inspiring feature in the whole annals of the earth. Man, with all his pride of life and reason, is still, as it were, only 1 For references to papers on this subject, see Knowledge, vol. xxii. (1899), p. 270.

Q

upon the threshold of his career. All the enormous periods that have gone before, with their struggles between this and that class of living creatures, culminate in the Post-Pliocene period, with the predominance of a being who seems capable of controlling his own surroundings, and of forging out new lines of progress for himself. In view of the long past, beside which human history is absolutely insignificant, the differences between individual men seem indeed of the most trivial character; and we may look forward with confidence to the work which Man as a race may yet achieve.

We now see how much William Smith and his fellowworkers have added to the interest and value of our fossils. If we begin to examine any collection, we find that even fossils must first be studied in the open-air. We must not be content with the bringing together of chance specimens, preserved as curiosities by a past generation, or picked out of the rubbish of a lumber-room; we must collect intelligently for ourselves, sampling our district bed by bed, and comparing the general aspect of the fauna, when we return home in the evening, with the drawings and descriptions in the text-books. The determination of the exact species of a fossil is often a work of care and time, and we may have to visit our nearest scientific library, to refer to the figures prepared by the original author of the specific name. No one can be expected to carry the details of hundreds of fossils in his head; and too much attention is often given to the learning off by heart of lists of species, when a few lessons in zoology, and in the general characters of successive faunas, would far better fit a student for appreciating Nature in the field.

We are by this time not only armed with the means of assigning any particular fossiliferous series of strata to its correct epoch in the world's history, but we can also detect, through the evidence of fossils alone, the occurrence of any considerable unconformity. If we find, for example, Triassic fossils in a bed which rests upon one containing Devonian fossils, we know that the intervening Carboniferous and Permian beds were either swept away by denudation before the Trias was laid down, or were never deposited in this locality, owing to some upheaval that occurred at the close of the Devonian period. We must always remember that we may find a fresh-water and a marine type of every system, while estuarine beds elsewhere unite the features of the two, besides containing shells characteristic of brackish water.

In due time the history of the most complex district can be unravelled, and we learn how many processes of construction and destruction have been required to produce the surface-features that we see around us. Stratigraphical geology" becomes, in fact, "Historical geology"; and any notes that we may make on the beds in a local section, and on the fossils that we discover in them, may prove to be a serious contribution towards the completion of the annals of the earth.

FIG. 24.-DIAGRAM OF HISTORY OF LIFE ON THE EARTH (see p. 241). The appearance of man is placed as far back as seems at present possible.

CHAPTER IX

THE SURREY HILLS

To apply the ideas gained in the last chapter to a special instance, we can scarcely do better than to visit the country to the south of London. There are few regions more simply beautiful, and few better known to the millions of dwellers in the south-eastern counties of England.

Whether we reach the hills of Surrey by the London and Brighton Company's Portsmouth line, or by the South-Eastern Railway to Red Hill, the features traversed are much the same. We pass the brown gravel cuttings in the suburbs, the oozy clay-banks towards Croydon, and then emerge upon an open rolling country of dry chalky fields, leading up to clumps of little woods; the church-spires set among them upon the rising ground show where the old villages have clustered. There is a steady incline from London southwards, until we reach bolder hills with white chalk cuttings through them; and at last the railway has to tunnel through a ridge, at Mickleham in the one case and at Merstham in the other. When we come out into the air again, we find ourselves leaving the face of a fine green range; a lowland, well wooded, with ponds and brickyards scattered in it, stretches for a few miles before us; and then the ground rises again in the distance towards broken and firclad summits.

If we reach Dorking, we can climb the highest point in the area, and make our survey from it, as we did from the Puy de Pariou in Auvergne. Five miles south of the town, Leith Hill rises, 967 feet above the sea; and we make our way through the forest-land towards it, with a singular sense of freshness after the traverse of suburban London.

From the summit we look over into several counties, including the whole of Surrey and its hills. Nearly all Sussex lies before us, and the borders of Kent are in the east. The features immediately around us are repeated, moreover, in