Ixviii PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



The limits of these two formations lie bet\^een the Triassic and 

 the Oxford clays, the latter known under the local name of Argile, 

 or Dives clay. The author quotes M. Hebert as having pointed 

 out that a long period of time must have elapsed between the 

 close of the Tipper Oolitic and the commencement of the Oxford 

 clay period, during which the former became indurated and sub- 

 sequently eroded on the surface ; for wherever the contact was 

 observed between the Oxford clay and the Great Oolite, the 

 existence of numerous holes, caused by rock-boring mollusks, was 

 noticed, as well as Oysters and Serpulse adhering to the surface. 



The author divides the Liassic system in Normandy into three 

 groups : — 



1. The Calcaire de Yalonges, or Infralias. 



2. The Gryphcea-arcuata limestone, or Lower Lias. 



3. The limestone with Belemnites and Gryplicea cymlium. 



The clays generally known as Upper Lias, he thinks ought, on 

 palseontological grounds, to be referred to the Lower Oolitic sys- 

 tem. The Calcaire de Yalonges is again subdivided into three 

 series, in the lowest of which are certain dolomitic beds, which 

 M. Eudes Deslongchamps looks upon as probably representing in 

 Normandy the Avicula-contorta beds, which everywhere form the 

 base of the Infralias. 



It will be remembered that M. Eenevier, basing his views on a 

 very careful examination of the Yaudois Alps, near the eastern 

 extremity of the Lake of G-eneva, also shows that the true Infra- 

 lias overlies the Avicula-contorta beds. 



The Lower Oolitic system is divided by the author into four 

 groups : — • 



1. Inferior Oolitic marls. 



2. Inferior Oolite. 



3. Fuller's earth. 



4. The Great Oolite. 



These again are subdivided into various series, all of which are 

 carefully described. The Great Oolite, however, is the most 

 extended, the most developed, and the best characterized of all 

 the Jurassic deposits in this region ; it almost invariably rests 

 upon the Fuller' s-earth, and has a thickness of at least 40 metres. 

 The sea-bottom is thus shown to have been continually sinking 

 since the period of the Inferior Oolitic marls, and deposits of great 

 thickness replace the former thin beds, deposited in ill-defined 

 basins, the limits of which were easily modified by the smallest 

 oscillations of the earth's surface. 



In describing the principal features of the Great Oolite, M. 

 Eudes Deslongchamps makes an observation so suggestive, that 

 I have no hesitation in reproducing it here, namely, "At the com- 

 mencement of this new period (Great Oolite) the fauna appears 

 very poor ; the first or lowest deposits are almost void of organic 

 bodies, at least in a portion of the Gulf. Fossil remains only 

 occur occasionally, around certain reefs, and the prevailing forms 

 are chiefly Lamellibranchiata and Polypi : but at a later period, 



