The rocks on this side of the channel are not indeed everywhere so well displayed, nor do they crop out with the same successive regularity as in Britain. Over extensive districts some disappear altogether, while in other places patches are seen lying out of their due order of superposition; not that in these instances the order is ever violated, but that some of the intermediate members seem to be wanting, and the remoter ones are in consequence found in contact. Still they conform to each other in their great line of section, and occupy the same constant relative position in their respective basins. Here, as in England, the Oolitic system embraces the Cretaceous, and extends in a larger semicircle round Paris as a common center, stretching from Ardennes to Normandy. The Lias, again, is inferior to the Oolite, and, filling a wider space, reposes on the transition slates of Virreville on the western coast. The Plastic clay, London Clay, and freshwater beds emerge in succession, and maintain each their corresponding dimensions. A remarkable grouping of rocks, illustrative of the order of superposition, occurs within the circuit of a few miles in the immediate vicinity of Boulogne, where resting upon the mountain limestone the following series may be observed: Coal, Oolitic marble, Purbeck and Portland stone, Iron-sand, Wealden clay, Chalk marl, Green sand, and Chalk. The Plastic clay reposes upon the chalk at Calais on the east of this group, and on the west stretches along the coast from Etaples to Treport.
The period during which the two countries continued to be united superficially, extended down at least to the last great upheaval of the bed of the ocean, subsequent to the Pleiocene deposits, and probably even after the establishment of the current epoch. The different formations we have been tracing are geologically connected over vast tracts of country; these tracts once formed basins or inland seas, into which their several suites of materials were drifted; the extensive regions of the older formations were amply fitted to inclose them; and, when the uppermost or pleiocene series of the English beds were deposited, one and the same shores and waters must have been common to the two countries—to the now insular as well as to the continental basins of the closing tertiary age.
One feels a real and enhanced pleasure in his researches, and his speculations assume a wider and a loftier range, as he casts a glance back to the white shores of Britain, and around upon the aspect of the country before him, and sees that he is still treading the same soil, threading his way among the same rocks, ascending and descending the slopes and valleys of the same earthy accumulations, varied only by slight local causes. Embarked upon the Seine, and along the banks of that lovely river, there is laid open for inspection a series of deposits, with every one of which we are already acquainted. The resemblance is even more striking when we examine the vast undulating plains around, and find the depressions, elevations, hills, and general outline of surface all of a class; and when we observe also the rocky foundations beneath to be one and the same—extensions merely of the same series of deposits, and forming at no very distant geological period integral portions of one great continent.
Combined with the subterranean movements which occasioned the dislocations, and inversions often, of the strata on both sides of the channel, the action of oceanic currents and incessant beating of the waves may be looked to as the instruments which produced their severance. The proofs are ample of the encroachments of the sea upon the eastern coast of England, the sites of towns, villages, and extensive fields, as marked on maps, now forming sand-banks, islands, and marshy swamps. The promontories and cliffs of Yorkshire, Norfolk, and Suffolk are still, as they were in Pennant’s time, “perpetually preyed on by the fury of the German sea;” the whole site of ancient Cromer is now under its waves; the towns of Shipden, Wimpwell, and Eccles, have entirely disappeared; large manors and even parishes have, piece after piece, been swallowed up; nor has there been any intermission, from time immemorial, in the inroads of the sea along a line of coast twenty miles in length, in which these places stood.[9] The ravages, from the same cause, have been equally if not more violent on the shores of the channel, the Straits of Dover, and the whole south coast; where slips of enormous magnitude are frequently recorded, cliffs undermined, and lands of considerable extent carried into the sea. The Isle of Wight, the peninsulas of Purbeck and Portland, the promontories of Devonshire and Cornwall, have all received their shape from the destructive agency, as they are still preyed upon and consumed by the tides and currents to which they are incessantly exposed. The French coast bears similar testimony to the inroads of the sea. From Calais to Cherbourg, with its magnificent dock-yard, the line of shore is everywhere indented and stripped bare, the strata undermined, and huge masses toppling over the abyss or rising into lofty pyramids of the most grotesque and varied forms. Britanny lies open, on every side, to the full swell of the Atlantic, where very recent as well as more ancient history attests the ravages of the waters in the destruction of towns and woods, the inundation of whole parishes, the severance of the hill of St. Michael from the main land, and, according to tradition, in the obliteration of the south-western district, of unknown extent.
Familiarized to facts such as these, and their necessary deductions, the mind no longer startles at the notion of the former physical union of the two countries. The agency seen in operation is demonstrably adequate to the effect. The straits are narrow. Their greatest depth between Dover and Calais is twenty-nine fathoms. The bed throughout is composed of the same stratum of chalk-rock, while a submarine chain extending from Boulogne to Folkestone is only a few fathoms under low water. Accordingly the wave of the mighty “ocean stream,” parted on the western coast, met tide after tide on the opposite banks of the connecting peninsula or narrow tongue of land, the one portion winding round by the Orcades and rolling up the German Sea, and the other portion beating on the line of cliffs facing to the west. The softer sedimentary deposits of the tertiaries would rapidly yield to the constant erosive action; the harder strata of the chalk, bared and undermined, would speedily follow; and thus, in a period comparatively short, the entire mass would be carried away, and the gulf of separation be irrevocably effected.
As a proof that France and England were united, and that these operations were continued within the human epoch, M. Desmarest, in his prize essay on this subject, proposed in 1753 by a society at Amiens, adduces the fact, that the noxious animals in both countries are identical, creatures which were not fitted to swim across the straits, and were not of a kind to be willingly introduced by man. But Desmarest in this only followed the views of an older writer, and from whose work, “Restitution of Decayed Intelligence,” all his facts and reasonings are obviously borrowed. This curious volume is the production of Richard Verstegan, written about two hundred and fifty years ago, and dedicated to James I. of Great Britain. The principal object of the author is to trace out the origin of the western nations, and more especially of “the most noble and renowned English nation,” as discoverable in their language and other antiquities. The fourth chapter of this quaint work is entitled, “How the Isle of Albion is showed to have been continent or firm land with Gallia, now named France, since the Flood of Noah.” Verstegan holds the doctrine that “in whatever manner and form it pleased Almighty God, in the beginning of the world, to divide the sea from the dry land, is unto us wholly unknown; but altogether unlikely it is that there were any isles before the deluge;” and to this event he ascribes the disruption of much of the dry land and the formation of islands. The connection of France and England continued long after this, and their severance, he believes, was produced by the operation of existing causes. The narrow isthmus by which they were conjoined extended across the Straits of Dover, just as Africa is united to Asia by the Isthmus of Suez, or North and South America by the Isthmus of Panama. This isthmus was breached by the action of the sea on both sides, but the sea being lower on the west side, the current swept with greater violence through this new channel, “toward the most huge Western Ocean, the greater divider of Europe and Africa, from the late found America.” He notices the identity of cliffs on the opposite sides of the straits, the submarine ridge which extends from Folkestone to Boulogne, the existence of marine shells all over the Netherlands and adjacent countries, and their consequent submergence before the sea was permitted to retreat through the new course produced in the isthmus, “and no way is there else to be found or imagined, whereby these seas might be drained or drawn away.” He refers to the identity also of the noxious animals in England and France, when our isle, continuing since the flood fastened by nature to the great continent, these wicked beasts did of themselves pass over; nor is the earthquake omitted by the writer, in his enumeration of causes whereby the sea, first breaking through, might afterward by little and little enlarge her passage; and the labor of man, too, had its share, when the inhabitants of the one side or the other by occasion of war did cut it, thereby to be sequestered and freed from their enemies.
Such is the train of illustration employed by Richard Verstegan, at a time when the state of the science of geology could furnish him with few helps; and but little indeed has been added by subsequent observers, except a few additional facts and inferences, which serve to confirm his conclusions. He remarks that such too had been the opinions of others, as of Antonius Volscus, Marius Niger, Servius Honoratus, the French poet Bartas, and our own countrymen, John Twin and Dr. Richard White; but these simply held the connection of the two countries as a matter of opinion, without laboring to find out “by sundry frequent reasons, that so it was indeed.”[10] England long dominated in France, crowned her princes Sovereigns of Navarre and the adjacent provinces, and Agincourt, Cressy, and Poictiers tell where man waged war against his fellow-man, over the remains of races long extinct, denizens of the same land, and propelled by instincts fierce alike for mastery or destruction. What a moral effect has been produced by the physical severance of the two nations, not only to themselves, but to the rest of the world! Great Britain, freed from the connection, can well afford to repose in peaceful majesty on her own shores, improving the arts, extending her commerce, and communicating, as the most noble and renowned nation the blessings of religion to the remotest parts of the globe.
II. Organic Remains. There are three districts in France which claim the special consideration of the geologist. The first comprises the basin of the Seine, of which Paris may be regarded as the center; the second is the basin of the Loire, extending in the direction of the rivers Gironde and Adour; the third is the volcanic district of Auvergue, embracing the tertiary and lacustrine formations, which have excited much geological speculation. The Silurian beds of Britanny are in many places absolutely loaded with Trilobites, which have found an able expositor in M. Marie Rouault; and the New Red Sandstone, which skirts the Vosges mountains, is equally remarkable for the fossils, vegetable and animal, peculiar to the Permian system.
The Basin of the Seine. The series of rocks included in this district, are described as the Paris basin formation, where, amidst their fossiliferous remains, the genius of Cuvier shone forth and captivated the world by his wonderful disclosures in the science of comparative anatomy. The deposits occupy a depression in the chalk upon which they rest unconformably, like those of the London basin: they agree generally in their organisms, but differ considerably in the quality of their respective materials. Blue clay with imbedded calcareous and argillaceous bands characterize the London formation, while that of Paris is distinguished by a superabundance of white limestones, marls, and gypsum. These rocks range over a vast extent of superficial area, being in their greatest length from N. E. to S. W. about one hundred and eighty miles, and from E. to W. about ninety miles. They belong to the Eocene period, consist of alternating groups of marine and fresh water strata, and have been arranged in the following order, according to the corrected diagram of M. Constant Prevost, who has considerably modified the earlier tabular arrangements of Cuvier and Brongniart:—Plastic clay, Calcaire grossier, Calcaire silicieux, Gypsum, Marls, Marine and fresh water strata.
The plastic clay and sand consist of intercalating argillaceous and gritty beds, containing a considerable quantity of lignite and fresh water shells. This deposit is not continuous throughout the basin, nor is it always lowest in position. In some places it rests upon a marine calcaire grossier, and in other places it is mixed up and imbedded in it, clearly showing that a river charged with argillaceous sediment entered a bay of the sea and drifted down, from time to time, wood and fresh water shells. No remains of mammalia have been detected in the plastic clay reposing on the chalk. The Calcaire grossier is composed of a coarse limestone, often passing into sand, and extremely rich in testacea, a locality near Gignon alone furnishing about four hundred distinct species. The Calcaire silicieux is a compact silicious limestone, almost destitute of organisms, and from its strong resemblance to the precipitates of mineral springs, as well as the fact that the few fossils contained in it are all of the land and fresh water species, it is justly inferred that the deposit is of fresh water origin. The Gypsum, with its associated Marls, is a saccharoid rock of considerable thickness, and constitutes the hill of Montmartre and other elevations toward the center of the basin. Here occur the remarkable variety as well as abundance of those organic remains which have given so much celebrity to the Paris basin. Fishes, reptiles, crocodiles, tortoises, birds, bats, mice, squirrels, opossums, gigantic mammoths, Anoplotheriums, and palm-wood, are all interred in this receptacle of the extinct dead. The remains of about fifty species of quadrupeds alone have been detected in the deposit, some of them, to the minutest organ, in the highest state of preservation—all of them extinct—and nearly four-fifths belonging to a division Pachydermata or thick-skinned animals. Immediately above the gypseous formation is an oyster-bed, of great superficial extent; this is succeeded by beds of sand, entirely destitute of fossils, forming a suitable covering to the countless millions which lie interred beneath.