'260 M. Desnoyers on the Chalk of the Cotentin. 



Lunulites cretacea . . . Defr Maest.,Tours,& Lewes. 



M//^.;.om (approach- l^jj^.^^^^^^^^ 

 ing anttqua JDeir.) J 



Pagrus proteus Defr Meudon, Tours. 



Alveolites Lam Picardy, Havre. 



Caryophyllia Mantell . . . Sussex, and Kent. 



Alcyonium glohulostmi . Defr Sussex. 



This table, though necessarily short and incomplete, never- 

 theless presents us with many important results. We in the 

 first place remark more than thirty species recognised else- 

 where as alone belonging to the chalk formation, some to the 

 upper chalk, {Bclemnites vmcro7iatus, Ananchitcs ovattis. Cra- 

 nia) ; others, and these form the greater number, to the mid- 

 dle chalk [craie moyenne) ,- and some, though peculiar to the 

 baculite limestone, more nearly approach the fossils of the 

 chalk, than those of any other formation. 



A second and equally essential observation is, that while 

 determining the species in the most careful mode possible, 

 whose analogues I have pointed out in equivalent rocks, slight 

 diiferences have presented themselves, which were at least suf- 

 ficient to form varieties. 



Another fact worthy attention, is the absence of many genera 

 and species alone found in this formation in the neighbouring 

 basins. Such are the Tun-ilites, Gryphcea colomba^ G. striata, 

 Ostrcea carinata, &c. &c., and especially the zoophytes, of the 

 genera Chenendopora, and Halliroa (Lam''.), Ventriculite and 

 Spongus (Mantell). This negative fact is another point of re- 

 semblance between the baculite limestone and the Maestricht 

 chalk. 



After such strong arguments as those deduced from relative 

 position and organic remains, which have so perfectly agreed 

 in proving the geological identity of the baculite limestone 

 and the chalk, it may perhaps appear superfluous again to 

 notice so secondary and accidental a circumstance as that of 

 the nature of the rock itself, especially in such a rock as the 

 chalk, in which is found such a variety of composition, tex- 

 ture, colours, and elevations above the sea. 



The chalk has generally been considered exempt from the 

 compactness common to so many other secondary rocks, or at 

 least as having presented but few examples of it ; and yet it 

 will perhaps be seen that it is not a greater rarity than in the 

 Calcaire grassier and the Jura limestone. This modification 

 of the chalk occurs under various circumstances, and equally 

 in all its divisions. Thus we see two isolated deposits of white 



chalk 



