284) Prof. A. Leymerie on the Lower Greensand 



here in a very succinct manner the chief of these reasons, and 

 to oppose them to those which Dr. Fitton on his side adduces. 



The chalk formation of Champagne is divided, first, very 

 distinctly, into two principal parts, one of which, our c/ial/k 

 properly so called^ is formed, in fact, throughout its whole 

 thickness, only of the rock mineralogically called chalk. It 

 corresponds exactly to the chalk of England, as Mr. Mantell 

 has described it. 



Between this stage and the Jurassic system is seen a series 

 of very varied strata and very rich in fossils, in which we can 

 distinguish two more new stages separated palaeontologically 

 by a stratum of a remarkable constancy throughout France, 

 and which is characterized principally by the Exogyr a sinuat a. 



The lower stage on this horizon represents the Neocomian 

 formation of Switzerland, and offers a multitude of peculiar 

 fossils, only some of which exist also in the lower greensand 

 of Great Britain. 



The bed above the Exogyra sinnata, comprising also this 

 last layer, corresponds to the greensand of the English, whose 

 subdivisions are not found here, although the thin layer con- 

 taining the Exogyra sinuata has strongly- marked relations with 

 the lower greensand. 



The two lower beds which we have just distinguished ac- 

 cording to the fossils, and which also differ greatly as to mi- 

 neralogical characters, have been separated moreover by a 

 geological ph^enomenon, rather slight indeed, but which has 

 left very marked traces in Champagne. These traces, which 

 we have specially mentioned in a note inserted in the Biilletin 

 (vol. i. 2nd series, p. 40), consist principally of an unconfor- 

 mity of stratification : thus near Chaource, for example, we 

 see the clays with Exogyra sinnata, and the greensand, quite 

 entire, reposing at the foot of an elevated hill constituted of 

 the Neocomian. 



This last formation then constitutes in the Aube, and we 

 might say also in the Jura, in the south of France, and as far 

 as the Crimea, a well-characterized type, which it would be 

 proper in all cases, were it even the contemporary of the 

 lower greensand, to consider apart as the principal type of the 

 lower cretaceous formation. Let us now examine whether 

 this synchronism can be admitted. 



If we transport ourselves into the south-east part of England, 

 we see, in a circumscribed space, a large deposit of fresh-water, 

 principally sandy and clayey, which is comprised between two 

 absolutely marine formations, one of which (Portland stone), 

 almost exclusively calcareous, finds its repi'esentative in our 

 countries in the compact and oolitic limestones which we de- 



