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.