172 



UPPER, OR FLINTY CHALK. 



broad annular flints occasionally found on the ploughed lands of the 

 Downs, and which bear considerable resemblance to a coit; their origin is 

 however satisfactorily illustrated by the specimen, fig. 1. Tab. xii. In this 

 example, the ventricuhte is inverted, and attached to the chalk by its 

 inner surface, the outer integument forming a narrow zone round the 

 annular flint, which in the perfect state of the fossil encircled the stem ; 

 as is shewn in the annexed sketch. 



The appearance of this specimen seems to warrant the conclusion, 

 that at the period of its mineralization, the silex was in a state of a thick 

 viscid fluid, otherwise it is difficult to understand why it should not have 

 extended to the margin of the zoophyte, instead of being consolidated in 

 its present situation. The cyathiforra flint, fig. 1. Tab. x. might also be 

 adduced in support of such an opinion, since the silex not only fills the 

 cavity of the ventricuhte, but is elevated considerably above the margin, 

 as if a pulpy or glutinous fluid had been gradually poured in, till the cup- 

 hke cavity was overflowing. 



Tab. xii. fig. 2, exhibits the external surface of a ventricuhte, attached 



