1852.] 



LYELL BELGIAN TERTIARY FORMATIONS. 



293 



Several species of Formninifera {Nodosaria, &c.) and several Bryo- 

 zoa are also in M. de Wael's collection from this deposit. 



Of the above 65 species of fossil niollusca, all but 16 are found in 

 the Suffolk Crag. This number of exceptions, however, is greater 

 than in the former lists. Most of them are marked as very rare by 

 M. de Wael, and several of these are Rupelmonde Clay species, which 

 may have been washed out of that older formation, such as Cancel- 

 laria evulsa, Typhis cimiculosus, and Venus incrassata. In regard 

 to Cardium turgidum, a Barton shell, I had no means of comparing 

 it with British specimens. 



The proportion of coralline crag shells is 42 out of the 65 species, 

 while there are only 28 common to the red crag. This preponde- 

 rance of coralline crag species is in favour of the somewhat greater 

 antiquity of the crag noir. The proportion also of recent species, 

 30 in &h, or about 46 per cent., is less than in the upper and middle 

 crag of Antwerp. This would indicate a period more remote from 

 our times, if we could feel sure that several of the extinct species, 

 which are so extremely rare, have not been derived from older beds. 



On comparing Tables III. and IV., it will appear that 30 species 

 are common to the crag gris and crag noir, which, when we consider 

 the total number of known species as fragmentary representations of 

 the marine fauna to which each respectively belongs, indicates a very 

 close approximation in age for the beds in question. 



Table VI. 



Showing the number of fossil species of Mollusca in the three divi- 

 sions of the Antwerp Crag, and their relation to the Suffolk Crag 

 and Recent fauna. 



Upper or yellow crag of Calloo* 

 Upper or yellow crag of Steu- "1 



venbergt / 



Upper crag of Calloo and Steu- \ 

 venbergunited(Tabs.II.III.) j 



Middle cragj 



Lower crag§ 



Number of 

 species. 



m 



52 



81 



94 

 65 



Coralline. 



46 

 39 



56 



71 

 42 



Red. 



59 



37 



68 



28 



Recent. 



37 

 31 



46 



46 

 30 



§ 4. Sands and Iron-sandstone of Biest (B. 2. Table I. p. 279). 

 Systeme Diestien of M. Dumont. 

 The series of ^vliich I have next to speak has been named by 

 M. Dumont from the town of Diest, about thirty miles N.E. of 

 Brussels, where the strata are of considerable thickness, but where 

 they have yielded as yet no fossils. They consist for the most part 

 of ferruginous sands and beds of a brown iron- sand stone, with occa- 

 sionally quartzose sands abundantly mixed with green grains, and 

 sometimes of a dark green or bright green glauconiferous sand. 



* See Table II. t See Table III. 



See Table IV. § See Table V. 



