'4f On the Mlniyraloglcal Geography 



On adiling those which we ohscrved ourselves, to those 

 %vhich have been collecttd by M. DetVance, we extend to 

 the number of fifty the various species of fossils with 

 which we are acquainted in the chalk, of the soils which 

 are the objects of our study. 



All the species of these fossils have not been as yet de- 

 termined, and we shall give in our subsequent detailed Me- 

 moirs their precise enumeration and determination: we 

 shall content ourselves with saying on the present occasion^ 

 that we have found 



Two lituoleles. 



Three vermiculitcs. 



Some belemnites, which, according to M. Defrance, ar© 

 diflercnt from those which accompany the ammonites of 

 compact lime. 



Some fragments of shells, which, from their tubular form 

 and fibrous structure, cannot be referred to any other than 

 the genus pinna: but if we were to infer from the thickness 

 of these fragments the size of the individuals to which they 

 must have belonged, we must conclude that these testacea 

 nmst have been monstrcais. We measured pieces 12 milli- 

 metres (•47 inches) thick, while the thickness of the largest 

 kinds of pinna known is only two millimetres (-08 inches). 



One muscle shell. 



Two oyster ditto. 



A species of the pbina genus, 



A cranium. 



Three anomites [tcrehrafulcs)» 



One spirorhis, 

 . SoniQ a?i an chiies, the crustaceous envelope of which has 

 -remained calcareous and assumed the sparry texture, while 

 tiie middle part only is changed into silex. 



Some porpytes. 



Five or six different polypwrs : one of them seems to 

 belong to the genus caryopliyilcea, and another to the genus 

 willepora. This last is jrenerally brown, and in the state 

 of oxidated iron, resulting from the decomposition of 

 pyrites. 



Lastly, some teeth of squali. 



We shall observe with M. Defrance, that there has not 

 Veen found in chalk any univalve shell with a simple and 

 regular spire. This fact is the more remarkable, as we 

 meet with these shells in great abundance, some metres 

 (39'3S inches) above the chalk, in calcartous strata a^sOji 

 tut of a different structure. 



Among the quarries and hills of chalk which we have 



visited;, 



