94 On the Geographical Extent of [Feb. 



known under the name of Brie, is, on the contrary, damp, and 

 covered with marshes, owing to the clays which accompany the 

 siliceous lime-stone, and the buhr-stones with which the soil is 

 almost every where covered. 



The sandy strata of the second marine formation has not (as 

 a predominating formation) a sufficient geographical extent to 

 constitute a physical region ; but all the elevated plains where it 

 appears are covered with vast forests. 



The Beauce, or the great elevated plain of fresh-water lime- 

 stone between the Seine and the Loire, is remarkable for its 

 uniformity, and the almost exclusive culture of corn (graines 

 rereates). 



The sandy deposit which covers the fresh-water lime-stone 

 constitutes to the south-east of the Beauce a particular region, 

 corresponding with the country generally called the Gatinais, a 

 low damp country of little fertility, and for the most part covered 

 with forests. 



This same sandy soil, mixed with the mud deposited by the 

 Loire, supports vineyards of such a considerable extent along 

 the river from Orleans to Blois, that it may be considered as a 

 small physical region separating the Beauce from the Solagne. 



What has been stated of the physical and geological consti- 

 tution of the part of the basin situated to the south of the Seine 

 is sufficient to indicate that of its limits in those countries. I 

 will therefore content myself with a rapid view of them. 



We have seen in the work of MM. Cuvier and Brongniart 

 that these limits could be traced decidedly from Mantes to 

 Epernon. It is the same as far as Gue-de-Longroi to the east of 

 Chartres, where the right bank of the Voise offers an inclination, 

 which constitutes the border of the Parisian formations, opposite 

 to the chalky plain of the environs of Chartres. This plain, as 

 well as those to the north of the Seine, is at first low, and even 

 rather rising towards the hills of the Perche. 



The limits then run in a direction towards the south-west, 

 passing near Bonneval, and follow, at a certain distance, the 

 course of the Loire as far as opposite Vendome, when they turn 

 towards Blois. But here there is no real physical demarcation. 

 The soil of the Parisian strata is almost on the same level as the 

 chalky plain, a circumstance caused by the cessation of all the 

 inferior formations, as before stated. 



From this point it becomes very difficult to trace the real limits 

 of the strata of the Paris basin on the south of the Loire, because 

 they are lost under the sandy deposits of indeterminate origin 

 above mentioned. However some affieurement, and the artificial 

 openings of quarries, discover the fresh-water lime-stone all 

 along the left bank of the Loire, from Blois to Cosne, but with 

 this difference, that the chalk which was concealed by the sand 

 in the northern part of the Solagne rises above Gien, and forms 

 elevations on both sides of the Loire, which inclose the small 



