Here are all things once more assembled, and as the tree of knowledge no longer bars from the tree of life, we can innocently search into all the mysteries, and see all the qualities and shapes, of every earthly object.
Nor is London less privileged and distinguished by its geological treasures and multifarious condition of things beneath. The capital stands on the tertiary Eocene strata, or last of the rocky series of the island. The pre-Adamic arrangements all here cease, the boundaries betwixt the old and the new world are here drawn. The age of humanity dawns. And, interred in the deposits immediately below, lie the last of a series of monsters which preceded man’s introduction upon the stage, and between whom and all his race an unequal war of merciless extermination must have prevailed. The reasoning animal, indeed, at once the most helpless and most potent of nature’s offspring, could but ill have existed under a constitution of the elements which fostered the Palæotheriums and Chæropotami of the tertiary age.
Neither the romance of geology nor the era of prodigies, therefore, are yet over. The curtain once more requires to be lifted from the dark regions of the past, ere we approach the arrangements, forms, and distribution of animal and vegetable life, of the epoch in which our own lot has been cast.
I. The Tertiary Group consists of a series of well-marked and closely connected beds of clays, sands, gravel, brecciated conglomerate, marls, and limestones; some of which are of marine, and some of fresh water origin—points only to be determined by their respective fossil remains. Some lithological distinctions may also be established; the marine deposits are less minutely laminated than those of the fresh water; and also, in general, the beds are thicker, and their sediments more confused in their arrangement. “Limestones, and fine light-colored clays,” says Mr. Phillips, “constitute the principal mass of the fresh water sediments; while sands, and blue and variously-colored clays, more particularly mark the marine depositions. The latter appear like the products of littoral agitation, as if the wearing of cliffs of older strata had furnished the materials of these newer rocks; while the former resemble the accumulations from the wasting surface of chalky and argillaceous countries.”
These deposits lie in hollows and depressions of the chalk formation, and constitute what is termed the London basin. A similar series of materials occur in Hampshire, separated from the former by the upraised edges of the subjacent strata, which, cropping out in like manner on the south, inclose them also in a basin-shaped area. The same arrangement prevails across the channel, where a suite of rocks referable to the same age lie within the chalks, and constitute the well-known Paris basin, whose remarkable remains were first brought to light from their tomb of ages in Montmartre by M. Brongniart and Cuvier, upward of thirty years ago. The Auvergne basins, in central France, are equally well characterized. And, stretching onward through southern Europe, the tertiary deposits occupy positions nearly similar; and all composed, with slight local variations, of kindred fossils and sediments.
Geology has been compared to history. We also see how it embraces the whole range of physical geography, restoring the land-marks of the past, and presenting pictures of the earth’s surface which the mere traveler can no longer detect. The rolling Thames, with town, spire, and villa nestling in every slope, and tunnel, bridges, and
“Crowded ports,
Where rising masts an endless prospect yield,”—
we seek in vain for on the geological map of the period. There were spice islands, with aromatic gales, palm trees, dates, turtles lazily pacing the sands, and crocodiles heavily climbing the banks, or plunging and gamboling in the deeper pools. A Polynesia, with a tropical climate and corresponding luxuriance of vegetable and animal life, occupied the intermediate regions of Europe and Western Asia. On the south and west a vast continent loomed over the main, whence, in part at least, the detrital matter of the several basins alluded to was derived; and there, too, in all probability, the source of the spasmodic action which successively elevated and depressed the bed of the sea on which were accumulating the tertiary deposits, and whose throes finally terminated in its own submergence, and upheaval of the south-east coast of Britain, and the whole of central Europe. Gulliver returned with a report of strange people, flying islands, and fertile descriptions of impossible monstrosities. Geology deals in a simple shifting of the scenes, new arrangements in the drama of creation, and is entitled to credit in its boldest assumptions, furnishing proof, as it abundantly does, from the existing wreck of those vanished realities to which it now assigns local habitation and name. London occupies the bottom of an ancient sea, whose spoils, six or seven hundred feet in thickness, are there to attest the fact; and for miles around, every excavation into the marine mass multiplies the evidence, and repeats the story of its existence.
The plastic and London clays constitute the lower beds of the series immediately above the chalk, and are nearly co-extensive in their range. From Reading on the west, these sediments stretch eastward through the valley of the Thames along the right bank to Margate; on the left, they cover the entire district to Ipswich; and constitute a very large part of the soil of the adjacent counties from Norfolk to Hampshire, prevailing more especially through the central and eastern districts. Mr. Prestwick has recently shown, that the lower English tertiaries form several distinct subdivisions, each marked by different conditions, and these conditions indicating ancient hydrographical and palæontological changes of importance. A conglomerate bed of round flint pebbles, mixed with yellow, green, or ferruginous sands, extends almost uninterruptedly from the Isle of Wight to Woodbridge, in Suffolk; this bed underlies the London clay, intercalated betwixt it and the plastic clay, and forms a well-marked geological horizon, dividing this formation from the older Eocene deposits. It contains thirty known, and eight or ten still undescribed species of testacea, twenty of which are not found in the lower deposits, while all are nearly identical with those of the superior and London clay beds. The plastic formation thus embraces the London clay, as the chalk does both, which again in its turn is embraced by the oolites; whence the older and inferior systems all widen, and extend successively as the bed of the sea was elevated; and hence the basins were gradually narrowed and contracted as they approached the last and closing ante-human epoch.