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