298 EOCENE STRATA IN FRANCE. [Ch. XVI. 



A. 3. Gres de Beauchamp, or Sables 3. White sand and clay of Barton Cln% 



Moyens. Hants. 



MIDDLE EOCENE. 



B. 1. Calcaire Grossier. 1. Bagshot and Brackleshani beds. 



B. 2. Soissonnais Sands, or Lits Co- 2. Wanting. 



quilliers. 



LOWER EOCENE. 



C. 1. Argile de Londres at base of Hill 1. London Clay. 



of Cassel, near Dunkirk. 2. Plastic clay and sand with lignite 



C. 2. Argile plastique and lignite. (Woolwich and Reading series). 



C. 3. Sables de Bracheux. 3. Thanet sands. 



The tertiary formations in the neighborhood of Paris consists of a 

 series of marine and freshwater strata, alternating with each other, 

 and filling up a depression in the chalk. The area which they occupy 

 has been called the Paris basin, and is about 180 miles in its greatest 

 length from north to south, and about 90 miles in breadth from east 

 to west (see Map, p. 221). MM. Cuvier and Brongniart attempted, in 

 1810, to distinguish five different groups, comprising three freshwater 

 and two marine, which were supposed to imply that the waters of the 

 ocean, and of rivers and lakes, had been by turns admitted into and 

 excluded from the same area. Investigations since made in the 

 Hampshire and London basins have rather tended to confirm these 

 views, at least so far as to show that since the commencement of the 

 Eocene period there have been great movements of the bed of the 

 sea, and of the adjoining lands, and that the superposition of deep 

 sea to shallow water deposits (the London clay, for example, to the 

 Woolwich beds) can only be explained by referring to such move- 

 ments. Nevertheless, it appears, from the researches of M. Constant 

 Prevost, that some of the minor alternations and intermixtures of 

 freshwater and marine doposits, in the Paris basin, may be accounted 

 for by imagining both to have been simultaneously in progress, in 

 the same bay of the same sea, or a gulf into which many rivers 

 entered. 



Gypseous series of Montmartre. — To enlarge on the numerous sub- 

 divisions of the Parisian strata would lead me beyond my present lim- 

 its ; I shall therefore give some examples only of the most important 

 formations enumerated in the foregoing Table. 



Beneath the Gres de Fontainebleau, often called " Upper marine 

 sands," and belonging to the Lower Miocene, as before stated, we find, 

 in the neighborhood of Paris, a series of white and green marls, with 

 subordinate beds of gypsum, A., Table, p. 297. These are most 

 largely developed in the central parts of the Paris basin, and, among 

 other places, in the hill of Montmartre, where its fossils were first 

 studied by Cuvier. 



The gypsum quarried there for the manufacture of plaster of Paris 



