d53 Mr. Lyell on the Cretaceous and Tertiary 



ness of the fossil fauna of Faxoe, was produced more by geographical con- 

 ditions^ such, for example, as the local shallowness of that part of the cre- 

 taceous sea, than by any general change in the creatures inhabiting the 

 ocean, effected in times intervening between the formation of the white chalk 

 and the Faxoe limestone. 



We know from the observations of Lieut. Nelson, in the Bermudas, that 

 the decomposition of certain corals or calcareous zoophytes, produces chalk, 

 or a pure calcareous mud, which only requires a slight degree of consolidation 

 to be identical with chalk. It is on islands and shoals that such corals abound, 

 and are continually decomposing ; and the white mud thence derived, is 

 carried out and spread over the deeper parts of the adjoining sea. If any of 

 these deeply submerged parts should afterwards become shallow, whether by 

 upheaval from below, or by filling up with mud, they may also support corals 

 of the same species as those from the decomposition of which the chalky mud 

 was first derived ; while at the same time more chalk will continue to be 

 formed in the depths of the surrounding sea*. 



In this manner white chalk and coral limestone may be made to alternate, 

 or if not, they may both be formed contemporaneously in the shallow and 

 deep parts of the same ocean. It seems to me, therefore, that the shells and 

 corals of Faxoe, some of which are even there imbedded in true chalk, throw 

 great light on the state of the northern ocean during the cretaceous period, 

 and on the nature and origin of that remarkable deposit, the white chalk. 



The chalk of St. Peter's Mount, Maestricht, bears undoubtedly much re- 

 semblance, both in its mineral character and genera of fossils to that of Ste- 

 vensklint ; but Dr. Beck is of opinion that some of the upper cretaceous beds 

 in Belgium approach more nearly in their species of fossils to the Faxoe lime- 

 stone than the Maestricht depositf . 



Chalk and Boulder Formation of Moen. 

 I shall now pass on to the cliffs of the island of Miien, which are from 300 



* Since Lieut. Nelson's communications were made to the Society, and since the reading of this 

 paper, Mr. Darwin has brought home much valuable information respecting the growth of coral, 

 both in islands and the barrier reefs skirting continents, and has found that the disintegration of 

 the zoophytes, gives rise continually, and on a large scale, to pure calcareous mud, which, when dry, 

 resembles chalk. The same geologist informs me, that the excrement of certain fish of the genus 

 Sparus, and of inferior tribes of marine animals, which prey on coral, consists of impure chalk. 

 These fish are seen in great numbers feeding quietly on living corals, just as herds of herbivorous 

 animals graze on herbage, and on opening their bodies, Mr. Darwin found the intestines filled 

 with similar chalk. 



t See Proceedings of Geol. Soc, No. 43, p. 218. 



