the workmen before us would have to dig down 160 feet through this dense, waterproof London Clay, and then perhaps through 10 feet of sand, before they would reach the next underlying formation, the Chalk. Thus, then, at this spot we learn the approximate thickness of the London Clay. But what of the history and origin of the dull-looking soil which we are asked to observe with such interest? To some of our company such a question is strange and uncalled for. ""Twere to consider too curiously to consider so." Has not the soil come from the hands of its Divine Maker just as we see it? Is it not part of the original substance of the earth, called into existence in its present form by an act of creative will ? Such are some of the questions proposed to us. Let us state in reply the conclusions of those who have investigated the composition, history, and origin of this London Clay, and then look at the evidence for ourselves. This London Clay is neither more nor less than the mud of an ancient sea-bottom. It is the accumulated deposit of the slowlysettling sediment of a pre-historic sea. This ancient sea-bed has now become a land-surface, and is covered with a fair mantle of grass and with human habitations. It is, nevertheless, the grave of countless generations of created things. Into this mud have sunk and become buried the varied flora and fauna of an age once bright and exuberant with life. So true is it, as Shakespeare's Friar Laurence tells us "The earth, that's Nature's mother, is her tomb." Here, then, in these Middlesex landscapes, this Saturday afternoon, the wonders of the deep can be studied by us upon dry land as well as by those who go down to the sea in ships to dredge the Atlantic floor. Let us see what more we can learn from this old sea-bed, from which the waters gradually retreated ages since as the land was slowly elevated. Of the creatures that once lived in these ancient marine waters of the London Clay, more than 375 species have been dug up near London. These creatures were corals, star-fish, sea-urchins, crabs and lobsters, mollusks, fish (especially sharks), tortoises, and crocodiles. We may see some of them to-day at the Jermyn Street Geological Museum (open till ten o'clock on Saturday nights, as we have often found in the winter months).* Some fine nautilus shells in the wall-cases there will suggest to us startling thoughts as to the climate which once prevailed where we this Saturday afternoon are walking and Treading beneath our feet old Ocean's races. What was the geography of this Hornsey meridian and latitude at this ancient period, before our present land-surface existed? What was the configuration of land and sea at the period of the deposition of the London Clay? The question is not altogether a futile one. Nothing so accurate in kind as Mercator's projection is offered by geologists; but some important data have been obtained for answering the enquiry. Even the depth of the sea which filled this London basin can be estimated with something like certainty. Professor Rupert Jones, of the Geological Survey, calculates it at about 100 fathoms. The creatures which live in the seas are confined to certain zones of depth, he reminds us. The indication of sea-depth for the London Clay, as afforded by one particular species of fossil with a perforated shell, is that which we have already named-about 600 feet. Again, what of the shores and continents of this old geographical period which were washed by the sea of the London Clay, on the dry bed of which we are now walking, and which now forms the * For a classified list of the fossils from the London Clay in the neighbourhood of London, see Memoir to Sheet 7 of the Geological Survey, by W. Whitaker, B.A., Longmans, 1864; price two shillings. This publication gives the stratigraphical geology of the London Clay in Middlesex, &c., in detail, and introduces the reader to Mr. Prestwich's original and elaborate papers in the Quarterly Geological Journal, Vols. II., III., VI., and X. The Museums at Bloomsbury and Jermyn Street are at present deficient in the fossil zoology of the clay around London, the Hampshire series being chiefly represented. For a knowledge of the abundant and diversified fauna of Hampstead, Highgate, and Sheppey geologists generally are indebted to the incomparable private collections of Mr. N. T. Wetherell, of Highgate, and Mr. J. S. Bowerbank, of Highbury. The Londoner ambitious of fieldgeology may remember that although there are no natural sections of the clay formation near the metropolis such as the sea-shore affords to the fossil-seeker, there are always in progress excavations incident to railways, wells, sewers, and dwellings. Brickfields especially should be appreciated. surface soil in Middlesex? What of the terrestrial vegetation and animal life of this remote era? Here is the answer: The abundance and variety of the fossil plants that are found in the London Clay, indicate the existence of dense primeval forests. Their solitude was probably but little broken, except by the harsh notes of a few solitary birds of prey, or of some fishing-birds. In their dark depths lived the great tapiroid animal of this old geological period, passing, like its existing congener, the tapir of America, a lonesome existence, and satiating itself with the fruits, birds, and shoots of those trees with whose fossilized remains it is now found associated. Its only known companions were that timid hare-like pachyderm and the great boa-like serpent. In contrast with this desolation on the land, the water swarmed with life. Large crocodiles, accompanied by their constant egg-devouring enemy, the fluviatile turtle, sported in the rivers, and the sea teemed with a numerous population of testacea and fishes. The remains of the creatures living on the land were borne down by the rivers, and thus became commingled with those living in the sea. It was under this very sky that all these great tropicallike forests, and beasts, birds, reptiles and fishes, of extinct forms, lived and flourished.* Here, then, is a chapter in man's interpretation of Nature as we find her revealed in the Middlesex hills and plains around us. This is the archæology of the London Clay, and here are the buried races of an ancient world concealed in Nature's tumuli at Hornsey. We finish reading this extract just as the excavators who are at work before us have brought up with their windlass and bucket a large pumpkin-like body from a shaft they are sinking in the clay. We advance to look at it. It is an entire capital specimen of the septaria of the London Clay. The men call it "clay-stone," but it is known by other names in the vernacular, "turtle-stone" being the most descriptive. Another alias, and not a bad one, is "bald pate." This is as large as a human skull. What is the fossil called a septarium? This common fossil of the London Clay, the septarium, is a concretion of lime and clay, which generally encloses some organic creature, most commonly a crab or a lobster, the remains of which you sometimes find within it. We split up the one before us, to find the creature which may thus be enveloped. We find there is a cavity within, but the contents are too much shrivelled to be read Professor Owen: British Fossil Mammals, &c. Mr. Prestwich: The Ground Beneath Us. by the naked eye. It accordingly becomes the prey of the microscopists of our party, who will examine at home and report upon it to the Quekett or the Old Change Microscopical Society, and perhaps exhibit it at their next winter conversazione. These septaria of the London Clay are useful as well as curious and archæological. They are collected to make the Roman cement for the piers of bridges and other places where the action of water is to be resisted. They are principally to be obtained by dredging off the sea-coast. They are got off Hampshire, as well as at Harwich, the Isle of Sheppey, and Chichester Harbour. We may have observed the number of boats so employed off Walton-on-the Naze or Harwich during our summer holiday. And these septaria are ornamental as well as useful. This capacity results from their mineralogical history. Let us again look at the one we have just found. This nodule of clayey limestone gets its name from the divisions, or septa, into which it splits up as its habitat gets less moist. The contraction of the body, which has resulted from a growing dryness of composition, has created fissures in it, into which carbonate of lime has been deposited. It is these green veins of calcite which make it susceptible of polish, and a fairly ornamental object for the chimney-piece. What it can be brought to by cutting and polishing may be seen in the hall at the Jermyn Street Museum. A fine circular slab (near to the "Dying Gladiator") shows the calcite disposed with tolerable regularity through a darker base, producing in section a singular and interesting pattern. Let us now, as the shades of evening are falling over this Middlesex landscape, lift our eyes from this mysterious subterranean world of the London Clay, with its buried races of extinct zoological species, and look again round the horizon of to-day in the light of the ancient page of Nature before us! Around us are the terraces, banks, and shoals-no longer submarine-of an ancient sea, on the dry bed of which we are walking. This soil, which is now a land-surface for the use of the human world, is populous below with extinct fossil races which flourished before there was yet a 'man to till the ground." 66 What an insight into the wonderful history of Nature these familiar scenes in our London environs afford, if we but lift the veil and trace the lineaments of the underlying worlds! How vividly do the words come into our mind, and give embodiment to our thoughts "Hast thou entered into the springs of the sea? Or hast thou walked in search of the depth? Or hast thou seen the doors of the shadow of death? Hast thou perceived the breadth of the earth? * Where wast thou when I laid the foundations of the earth? Declare if thou hast understanding." We now begin to wend our way homewards, for over Crouch Hill and Highgate the evening mists are gathering. |