of Crelaceou.s Hocks. 165 



boutliern infiisory-marls, and of tLe northern beds of iiint, at 

 once presents itself to the mind. Thus, by means of this 

 changed relation, the formation of flint would receive its full 

 explanation. A greater age, as deduced from the conversion 

 of the infusory marl-beds into flint-layers, and from the greater 

 decomposition of the calcareous animals, and their conversion 

 into inorganic particles, might thus be assigned to the chalk 

 strata of the north ; but still, local circumstances might pro- 

 duce different effects at the same periods, as is, from other 

 circumstances (from the similar chalk animalcules, &c.), more 

 probable. 



6. The want of numerous and varied forms of sihceous in- 

 fusory animals in the chalk previously noticed by the author, 

 has now disappeared, and, in its place, gi-eat abundance has 

 presented itself. 



In all, the author has observed seventy-one different mi- 

 croscopic calcareous and siliceous species of animals in the 

 chalk; but, besides these, also numerous larger calcareous 

 animals ('l-24th of a line in size) and many included plants, 

 Tethyae, Sponges, Confervae, and Fuci. The vai-ied forms of 

 the genera Botalia and Textalaria of the Polythalamiae, ap- 

 ]>ear to him to constitute the great mass of the chalk of all 

 localities. He reckons altogether seven genera and twenty- 

 two species of polythalamic microscopic calcareous animals ; 

 and, moreover, microscopic and larger nummulites, cypridae, 

 &c. Further, he has hitherto determined forty species of sili- 

 ceoas infusory animals ^^hich belong to fovu-teen genera, with- 

 out including the eight forms previously enumerated, and 

 which \\ ere probably soft, and merely included in flint. He 

 lias found five species of plants containing silica. In the flints 

 of the Jura limestone of Cracow, he detected well preserved 

 peculiar Polythalamiae, and remains of Sponges or Tethyae ; 

 and lately, he has found Polythalamiae of the chalk in the 

 flints occurring in the gault which lies under the chalk at Cam- 

 bridge in England. 



A general table of these relations of the animals from the 

 chalk and chalk-marl of the fourteen localities observed by 

 him, and also specimens of the rocks, together with a collec- 

 tion of well-preserved microscopic preparations, containing 



