The geographical distribution of the respective rocks of France and Great Britain forms a remarkable coincidence in giving shape and contour to their general outline. Thus, the primary systems in both stretch along their western shores, presenting a vast barrier-wall of the oldest and hardest rock against the incessant encroachments of the Atlantic. Britanny and Normandy consist almost entirely of granite, gneiss, mica-schist, and silurian rocks; on these repose the upper suites of the secondary strata,—the lias, oolite, and chalk—training to the south and east. On the tertiary formations rest the secondary, narrowing in their basins, and preserving the same general line of bearing with the English beds, and in both cases reaching their maximum of thickness and exuberance of fossils around the capitals of Paris and London. The old red sandstone is not indicated on the maps, nor is it clearly ascertained to possess a habitat in the district in question. The coal-measures are of very limited dimensions, but in their due order of position at Hardinger, near Boulogne, and passing under the chalk and green sand, continue in an easterly direction by Valenciennes, Mons, Namur, and Liege, to Eschweiler, near Aix-la-Chapelle. The new red sandstone, of both divisions, is amply developed along the eastern boundaries from Semoy in Ardennes to Langrés and the borders of Switzerland. On the west again, the tertiaries prevail from the mouth of the Gironde to Bayonne on the Adour, where they are exposed to the constant tearing and erosion of the rude surges of the Bay of Biscay, while in the interior, and over the district of Auvergne, the granites and gneiss are widely overlaid by the overflowings of the most recent extinct volcanoes; the oldest and the newest plutonic rocks thus lying in immediate superposition and contact.