Ch. XVII.] maestkicht beds. 315 



lower cretaceous (or Neocomiari). 



B. 1. Lower Greensand — green sand, iron sand, clay, and occasional beds of lime- 

 stone (Kentish Bag). 

 2. Wealden beds or Weald clay and Hastings sands.* 



Maestricht Beds. — On the banks of the Meuse, at Maestricht, re- 

 posing on ordinary white chalk with flints, we find an upper calca- 

 reous formation about 100 feet thick, the fossils of which are, on the 

 whole, very peculiar, and all distinct from tertiary species. Some few 

 are of species common to the inferior white chalk, among which may 

 be mentioned Belemnites mucronatus (fig. 290, p. 325) and Pecten 

 quadricostatus, a shell regarded by many as a mere variety of P. 

 quinquecostaius (see fig. 305, p. 327). Besides the Belemnite there 

 are other genera, such as Baculite and Hamite, never found in strata 

 newer than the cretaceous, but frequently met with in these Maestricht 

 beds. On the other hand, Voluta, Fasciolaria, and other genera of 

 univalve shells, usually met with only in tertiary strata, occur. 



The upper part of the rock, about 20 feet thick, as seen in St. 

 Peter's Mount, in the suburbs of Maestricht, abounds in corals and 

 Bryozoa, often detachable from the matrix ; and these beds are suc- 

 ceeded by a soft yellowish limestone 50 feet thick, extensively quar- 

 ried from time immemorial for building. The stone below is whiter, 

 and contains occasional nodules of gray chert or chalcedony. 



M. Bosquet, with whom I examined this formation (August, 1850), 

 pointed out to me a layer of chalk from two to four inches thick, 

 containing green earth and numerous encrinital stems, which forms 

 the line of demarcation between the strata containing the fossils 

 peculiar to Maestricht and the white chalk below. The latter is dis- 

 tinguished by regular layers of black flint in nodules, and by several 

 shells, such as Terebratula carnea (see fig. 301), wholly wanting in 

 beds higher than the green band. Some of the organic remains, how- 

 ever, for which St. Peter's Mount is celebrated, occur both above and 

 below that parting layer, and, among others, the great marine reptile 

 called Mosasaurus (see fig. 276), a saurian supposed to have been 24 

 feet in length, of which the entire skull and a great part of the skele- 

 ton have been found. Such remains are chiefly met with in the soft 



* M. Alcide d'Orbigny, in his valuable work entitled Paleontologie Francaise, has 

 adopted new terms for the French subdivisions of the Cretaceous Series, which, so 

 far as they can be made to tally with English equivalents, seem explicable thus : — 



Etage Danien. Maestricht beds. 



" Senonien. White chalk, and chalk marl. 



" Turonien. Fart of the chalk marl. 



" Cenomanien. Upper Greensand. 



" Albien. Gault. 



" Aptien. Upper part of Lower Greensand. 



" Neocomien. Lower part of same. 



" Neocomien inferieur. Wealden beds and contemporaneous marine strata. 



