It is, therefore, certain that the calcareous part comes exclusively from the sea, and even from the bottom of the roadstead of Cancale. As for the silex and clay, a part in their deposit may be attributed to the rivers; but it should first be understood how unimportant these three small rivers are, each discharging not more than an average of eight to ten _cubic metres_ of water per second. Farther, if the contributions of the rivers reckoned for anything in the deposits which are made in this locality, clayey or gravelly stratifications would be seen on their banks at the parts where the tide is least felt. Nothing of the kind occurs. The mixture of the calcareous matter, the grains of silex, and the argillaceous atoms is so intimate, that it is evident it could only be made at the very centre of the production of the calcareous matter; that is to say, at the bottom of the sea. If the fluviatile deposit was appreciable, it would counterbalance entirely, or in part, the calcareous overplus in the drift taken from the top of the roadstead, as compared with that taken at the bottom. Far from this being the case, the progression of the calcareous element, which can only come from the sea, is seen in proportion to the elevation of the shores. Finally, if the fluviatile deposit ought to be reckoned for anything, a larger proportion of clay would be seen upon the brink of the Sée, which traverses fissile lands, than in the neighbouring channel of the Couësnon, which traverses lands of a much harder character, furnishing less clay than the fissile ground of the Sée and the Selime. Now, the contrary is the case; the drifts of the neighbouring channel of the Couësnon are more clayey than the others, solely because this channel being more sheltered than the beds of the other two rivers, the muddy matter which the sea always holds so abundantly in suspension, and which it deposits in the basins of ports, can be carried there concurrently with the drifts. On making the same investigations for the Seine, it was found that the sands transported by this river do not pass Rouen, and that all the accretions that are seen lower down, as far as the flats which are met with at its mouth, are deposits by the sea. The same results were arrived at for the Scheld. As to the Meuse and the Rhine, the following deductions have been made.