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 374 forming a large portion of the floor of the Atlantic Ocean. Throughout the ages during which these Protozoa were slowly building up the white cliffs of Dover and the forelands of Beechy Head, some agency, at which we have hitherto done little more than guess, was busy at equal, or nearly equal intervals, laying down upon this living and snowy carpet those regular strata of isolated flint nodules which characterise the formation. The deposition of each layer was a work of considerable time, and their periodical appearance is not the least among the many puzzling difficulties which beset the question of their origin. We shall see presently how Dr. Wallich’s theory meets this part of the problem; but for the present we must confine ourselves to a more minute exploration of the locality from which the London flint and gravel is derived.

When the primeval Foraminiferæ had completed their great work, and the heaped-up shells of countless generations had accumulated into a stratum nearly a thousand feet in thickness, a change took place over the whole district comprised within the limits of the Wealden Valley. A gradual upheaval of the sea-floor began, and the “white cliffs of Albion” rose into the daylight, to play another and more conspicuous part in the economy of nature and the history of the world.

This upward movement was not effected with perfect uniformity, for the central portion of the ellipsis on our map was lifted first, while the hills which hem the Wealden in did not emerge till later on. The country rose, in fact, somewhat in the form of an inverted basin, the spot where Hastings stands being, perhaps, the first point which showed above the level of the ocean.

So slow was the ascent, and so nearly were the rate of upheaval and the erosive power of water matched, that foot after foot of the chalk was washed away by the waves as fast as it appeared; and this went on until the stratum was cut completely through over the apex of the basin and the beds below exposed to a similar action. Through the uppermost of these, too, the sea ate its way till the lowest member of the Wealden group, the green sand, had been uncovered. Meanwhile the North and South Downs, as a matter of course, receded farther from each other in every direction, until the progress of denudation was stopped by the increased activity of the upheaving forces which finally lifted the whole country above the destructive action of the ocean. The process may be aptly illustrated by making a series of thin successive slices at any part in the surface of an orange, the rind of which will represent the chalk, while the pulp beneath stands for the underlying clays and sand. Each cut of the knife exposes more and more of the substrata, and widens the white ring of peel just in the same manner as the denuding sea extended the area enclosed within the Downs. Since this operation ceased no geological change of importance has occurred. Man has come on the scene, and the picturesque hills and valleys of Hastings, the gently curving combes of Brighton and of Lewes, and the bold chalk escarpments which surround them, remain to delight him with their varied beauty or instruct him of their wonderful origin. Glancing again at the map, we shall be naturally struck by the enormous amount of material which has thus been washed away. The original chalk covering, some hundreds of feet thick, has been removed from whole counties and carried everywhither by the tides, the currents, and the storms. But the influences which disinterred could not so effectually distribute the huge mass of flint they gradually washed out from its matrix; hence, though the milky water holding large quantities of chalk in suspension was free to flow to any distance with its burden, the heavier nodules remained more nearly in the immediate neighbourhood to be broken, rolled, and rounded on many a beach into the smooth red and yellow pebbles which we know so well. The Wealden Valley, then, is the great original gravel-pit whence our minor local deposits are derived—the actual home of every shattered and abraded flint in London.

It would be too long a story to tell of their dispersion thence over the field they now occupy, or of the means used for their removal, though this is in itself a geological romance well worthy of a special chapter. When the winds and waves had done their best, the great ice-fields and bergs of the glacial epoch took up the business of their transportation, nor did this wonderful carrier cease his labours till tens of millions of tons of flints were scattered broad-cast over half our southern and eastern counties.

Here we will pause for a moment before our subject leads us into other climates, and among fresh creations, to review what we have advanced, and consider what conditions have been established with which any hypothesis explanatory of flint formation must of necessity agree. We have traced the materials of our garden-paths back a tolerably long way in their history, and marked both the locality in which they were elaborated and the agencies that first dug them from their chalky bed. We have further seen that they were deposited in a sea still in its profounder depths and differing in none of its essential constituents from the waters washing our shores to-day. There is no evidence whatever that the cretaceous ocean was highly charged, as some have assumed, with silex in a state either of fine division or solution; nothing indicates the existence of a larger per centage of any mineral matter in the seas of that period than is found in modern salt water. The Foraminiferæ, we may be certain, needed the same element then they want now, and the theory of gradual accumulation from a fluid surcharged with siliceous particles must be pronounced untenable. The chief remaining condition to be met is the periodical nature of the deposit; and this is a stumbling-block over which almost every previous explanation hopelessly breaks its neck. We shall see presently how the cetacean hypothesis stands this crucial test, and we now approach the history and evidence in favour of Dr. Wallich’s suggestions.

Sitting at our window writing these lines we have but to lift our eyes from the paper to be made powerfully sensible of the seemingly hopeless nature of the task we have undertaken.

In view of the numberless large and small stones, all fragments of chalk flints, which cover