These gravels may be assigned to a time—probably towards the conclusion of the Glacial epoch—when the climate of Britain was still cold, when the higher hills were permanently capped by snow, and when glaciers may have lingered in the more mountainous regions. All through the spring and early summer the rivers would be swollen with melting snow, the torrents from the highland districts would be full and strong, and thus denudation would be comparatively rapid—the more rapid because the latest deposits, the Boulder Clay with its associated gravelly sands, would be incoherent and in many places still unprotected by vegetation. Very different would be the brooks and the rivers which then traversed the valley of the Thames from those which now creep through lush water-meadows or glide “by thorpe and town.” The final sculpturing of the valleys—all that has been effected since the date of the Chalky Boulder Clay—may have been accomplished with comparative quickness. Still, since the time when the oldest of these flint implements were lost by their owners, the beds of the valleys have been lowered, in some places by not less than a hundred feet. The district also, until the greater part of this final sculpturing was accomplished, was inhabited by men whose habits of life were throughout substantially the same.
The alluvial deposits, as already stated, rise but little above the surface of the river at high tide. Their thickness varies, but commonly it is from about 12 to 20 feet. The lowest part is generally gravel and sand—materials indicating that the conditions which produced the older deposits of a like nature passed away gradually. This is followed by river silt, with occasional thin beds of peat or with indications of old land surfaces on which flourished woods of oak or even of yew. Below the Port of London, marine shells are rather abundant in the lower part of the silt; these indicate that the general level of the land was a little lower than it had been during the preceding age, perhaps even than it is at present. These alluvial deposits have yielded implements of smoothed or polished stone, of bronze and of iron; also canoes, and even relics of the Roman occupation of Britain. In other words, they have yielded antiquities belonging mainly to prehistoric times, though the record is continued up to a comparatively recent date. Marshy or peaty ground occurs even within the limits of the city,[6] as at one corner of St. Paul’s Cathedral, in Finsbury Crescent, and near London Wall, as well as at Westminster. Thorney—the “Isle of Thorns”—the site of the Abbey, was formerly a low insular bank of gravel among marshes. The lake in St. James’s Park indicates the track of the Tyburn, which traversed one of these swamps. It was a brook of some size, and traces of it may be found in the names Marylebone (le-bourne[7]), and Brook Street. One branch of it passed “through Dean Street and College Street till it fell into the Thames by Millbank Street.”[8] The water from the slopes north of Hyde Park made another stream called the Westbourne; this, after following a path still suggested by the Serpentine, found its way to the Thames through a fenny district which is now Belgravia (see also p. [26]).
Such, then, is the structure of the valley of the Thames; such are the deposits which form its surface on either side, and on which the metropolis has been built. But we must now look a little more closely at their distribution, for by this the growth of London in ancient times was largely determined. The broad terrace already mentioned on the left bank of the Thames, the site of mediæval London, consists, for a couple of miles or so inland, mainly of a flint gravel more or less sandy, seldom exceeding 20 feet in thickness, and commonly rather less, which rests upon the tenacious London Clay. Here and there this gravel may be traversed by a small stream, but the most marked break in its level is formed by a brook which, flowing from the slopes of Hampstead and Highgate, at last has cut its bed down to the clay and has broadened out into a creek as it joins the Thames. It was known in its lower reaches as the Fleet (see p. [27]). This gravel terrace made London possible; this stream formed its first boundary on the west. The rain-water is readily absorbed by the gravel, but is arrested by the underlying clay. It can escape in springs wherever a valley has been cut down to the level of saturation, but if it is not tapped in this way the gravel will be full of water to within a few feet of the surface, so that a shallow well will yield a good supply. The first settlement was placed upon this gravel, by the river-side, where the channel is still deep at high tide; it was limited on the west by the slopes descending to the Fleet, on the east by the lower ground which shelves downwards towards the mouth of the Lea. From this nucleus, enclosed within the Roman fortification, the town expanded, as times became more peaceful, along the lines of the great roads; and at an early date a tête-du-pont would undoubtedly be formed at Southwark.
But without entering into the details of this development, let us pass over some centuries and see how the growth of London was for a long time conditioned and limited by this gravel. The metropolis spread “eastward towards Whitechapel, Bow, and Stepney; north-eastward towards Hackney, Clapton, and Newington; and westward towards Kensington and Chelsea; while northward it came for many years to a sudden termination at Clerkenwell, Bloomsbury, Marylebone, Paddington, and Bayswater: for north of a line drawn from Bayswater, by the Great Western Station, Clarence Gate, Park Square, and along the side of the New Road to Euston Square, Burton Crescent, and Mecklenburg Square, this bed of gravel terminates abruptly, and the London Clay comes to the surface and occupies all the ground to the north. A map of London, as recent as 1817, shows how well defined was the extension of houses arising from this cause. Here and there only beyond the main body of the gravel there were a few outliers, such as those at Islington and Highbury, and there habitations followed. In the same way, south of the Thames, villages and buildings were gradually extended over the valley-gravels to Peckham, Camberwell, Brixton, and Clapham; while, beyond, houses and villages rose on the gravel-capped hills of Streatham, Denmark Hill, and Norwood. It was not until facilities were afforded for an independent water-supply by the rapid extension of the works of the great Water Companies that it became practicable to establish a town population in the clay districts of Holloway, Camden Town, Regent’s Park, St. John’s Wood, Westbourne, and Notting Hill.”[9]
It is possible that the position of the older parks—St. James’s, the Green Park—and Hyde Park may have been indirectly determined by the fact that over much of them the gravel is thin or the clay actually rises to the surface.
Every old settlement outside the earlier limits of the metropolis marks the presence of sand or gravel. Hampstead and Highgate, which early in the nineteenth century were severed from London by nearly a couple of miles of open fields, stand upon large patches of Bagshot Sand, which caps the London Clay and is sometimes as much as 80 feet thick. This yellowish or fawn-coloured sand may be seen almost anywhere in the old excavations at the top of Hampstead Heath, and the difference of the vegetation on this material and on the clay of the lower slopes cannot fail to be noticed. On the latter, grass abounds; on the former, fern, furze, and even heather. The junction of the sand and the clay is indicated by springs which supply the various ponds. These are occasionally chalybeate, like the once-noted spring which may still be seen in Well Walk, Hampstead. Harrow stands on another outlying patch of Bagshot Sand. Enfield, Edmonton, Barnet, Totteridge, Finchley, Hendon, and other old villages are built upon the high-level gravels which have been already mentioned.
The shallow wells are no longer used in London itself. Infiltration of sewage, in some cases of the drainage from churchyards, had rendered many of them actually poisonous; clear, sparkling, even palatable, though the water might be, there was often “death in the cup.” There was a terrible illustration of this fact during the visitation of the cholera in 1854. A pump, the water of which was much esteemed, stood by the wall of the churchyard in Broad Street (south of Oxford Street). The water became infected, and the cholera ravaged the immediate neighbourhood. But though most of these pumps were closed barely sixty years ago, some, like that in Great Dean’s Yard, Westminster, were in use for quite another quarter of a century. It has now disappeared, but that within the precincts of the Charterhouse is still standing. Thus London was limited to the gravel till it was able to obtain water from other sources.[10]
The first step in this direction was early in the seventeenth century, when the New River Company had its origin, and for many years this was the only Company by which water was supplied to London; but seven others were subsequently founded.[11]
The New River Company obtains its water from the Lea, the original source being nearly forty miles from London, but the supply has been since increased by sinking wells. The East London draws upon the same river. Five of the other Companies get their water from the Thames, some miles above London, augmenting their supply by means of wells, and the Kent Company draws exclusively from deep wells in the chalk. As these Companies were founded the metropolis began to spread rapidly over the areas which they supplied, but it did so in a regular and systematic fashion. Houses fed by the mains of a Water Company must keep, as it were, in touch with their base of supply, because of the cost of laying a long line of pipes to supply a solitary house. Thus a town which draws its water from mains advances block by block into the surrounding country, and is not encircled by a wide fringe of scattered dwellings.
In the London area, however, there is a way in which the occupant of an isolated house can obtain a supply of water, though it is not a cheap one. He may bore through the London Clay into the underlying sands and gravels. When a porous stratum rests on one that is impervious, the former becomes saturated with water up to a certain level, dependent on local circumstances, and in this case a well sunk sufficiently deep into it will be filled. But if the porous stratum be also covered by one which is impervious; if all three be bent into a basin-like form; and if the porous one crop out at a considerably higher level than the place where a well is needed, then it may be water-logged to a height sufficient to force the water up the bore-hole, perhaps even to send up a jet like a fountain. Wells of this kind are termed Artesian, from Artois in France, where they have been in use for several centuries, and they began to be sunk in England about a century ago. The London Clay was pierced, and the water-logged sands and gravels belonging to the lowest part of the Tertiary series were tapped. These basin-formed beds crop out at an elevation generally of about one hundred feet above the Thames; thus they were charged with water to a considerable height above the level of the river, and it very commonly at first spouted up above the surface of the ground; but as the wells increased in number, its level was gradually lowered, for the area over which these beds are exposed is not very extensive, and a stratum cannot supply more water than it receives by percolation from the rainfall. At first everything went well; consumers were like heirs who had succeeded to the savings of a long minority, for water had been accumulating in this subterranean basin-like reservoir during myriads of years; but after a time the expenditure began to exceed the income, and the water-level sank slowly, till now it is many yards below the surface of the ground.