TERTIARY FORMATION. PARIS BASIN. 7* 



which are in many instances analogous, or the same as those of 

 the eocene formations in other parts of the world. 



7. The geological position of the city of Paris resembles that 

 of London, each being situated upon an extensive and important 

 group of tertiary strata, which occupies a depression or basin in 

 the underlying chalk. The nature of the two deposits is, how 

 ever, totally different, the deposit being characterized in England 

 by-., great accumulations of argillaceous matter, which form the 

 London clay, while in the neighbourhood of Paris there is a varied 

 series of limestones and marls, alternating with important beds of 

 gypsum and silicious matter. 



8. The depression in the chalk forming the celebrated Paris 

 basin so frequently named by geologists, which is filled up by these 

 strata, is nearly one hundred and eighty miles in its greatest length, 

 and about half that in breadth. The surface of the chalk is usually 

 covered by broken and rolled flints, often cemented by a silicious 

 sand into a kind of breccia; and these flints seem to mark the 

 action of the sea upon reefs of chalk before the commencement of 

 the tertiary epoch. 



The order of stratification of the Paris basin is represented in 

 the following table. 



8. Upper marine sands. 7. Upper fresh water sands. 



6. Green marls. 

 5. Gypsum. 



, ( Calcaire siliceux, or o ( Calcaire grossier, or 



* I Fresh water limestone. ' ( Marine limestone. 



2. Plastic clay. 

 1. Chalk. 



9. Above the chalk we find, first, deposi^ of plastic clay, s>o 

 called because varieties of it are well suited for the manufacture 

 of pottery. In the neighbourhood of Montereau on one side, be- 

 tween Houdan and Dreux on the other, it is remarkable for its 

 whiteness and purity, and is used in the fabrication of the finest 

 porcelain. Around Paris it is coloured and impure, and suitable 

 only for coarse pottery. These clays contain lignite, in which we 

 see, perhaps for the. first time, mingled with numerous co'nifers, 

 phanerogamous monocotyledons, true palms, and some dicoty'le 

 dons. Marine, as well as fresh water shells, are found in its upper 

 part. 



7. In what respects does the geological position of Paris differ from that 

 of London. 



8. What is the extent of the Paris basin ? 



0. What lies next above the chalk in the Paris basin ? What art the 

 eharacters of plastic clay ? To what uses is it applied ? 



28 



