PART U. CHAPTER XV. 189 



Cretaceous Coral Reef ...................... Maastricht Beds. 



mata have been found in both. The Faxoe formation, however, 

 is not only remarkable for the number and good preservation of 

 its fossil corals, but also from the generic resemblance of many 

 of its univalve shells to forms . usually supposed to appertain 

 chiefly or exclusively to the tertiary period. Thus among the 

 patelliform univalves, we find Patella and Emarginula, and among 

 the spiral, the following genera, Cyprsea, Oliva, Mitra, Cerithium, 

 Fusus, Trochus, Triton, Nassa, and Bulla. 



The species however do not agree with those of the tertiary 

 strata, and are associated with cephalopoda of those extinct 

 families before mentioned as characteristic of the cretaceous, 

 and foreign to the tertiary epoch ; as, for example, the ammonite, 

 belemnite, and baculite. Two species, the Belemnites mucronatus 

 (Fig. 155.), and the Baculites Faujasii (Fig. 156.), being 

 common to the Faxoe beds and white chalk. 



From these facts, we may conclude that the Faxoe limestone 

 was formed in the cretaceous sea, in a spot favourable for the 

 multiplication of stony corals and univalve shells ; and as some 

 small portions of the rock consist of white earthy chalk, this 

 latter substance must have been produced simultaneously, and 

 some of it may have been washed away, in the form of mud, 

 from the coral reef of Faxoe, and dispersed over the deeper parts 

 of the same ocean, just as the white mud, swept out of the la- 

 goons of the Bermudas or coral islets of the Pacific, must form 

 deposits of white chalk, covering much wider spaces than those 

 occupied by the reefs. 



The same remarks apply to a rock, which reposes on the 

 Upper Chalk with flints, at St. Peter's Mount, Maestricht, and at 

 Ciply, near Mons. It is a soft yellowish stone, not very unlike 

 chalk, and "includes siliceous masses, which are much more 

 rare than those of the chalk, of greater bulk, and not composed 

 of black flint, but of chert and calce- 

 dony."* Like the Faxoestone, it is 

 characterized by a peculiar assemblage 

 of organic remains which are specifi- 

 cally distinct from those of the tertiary 

 period, but many of them common to 

 the white chalk. 



As these Maestricht beds have been 

 thought to be intermediate in character 

 Rkoto mag evsis, Between the secondary and tertiary for- 



, 

 Maestricht ; found by Count mations, it may be proper to mention, 



as opposed to this opinion, that the Am- 

 monite (Fig. 164.), Baculite, Hamite, and Hippurite, have been 



* Fitton, Geol. Proceedings, 1830. 



