102 FOSSILS FROM THE UPPER GREENSANb. 



It will be seen from the above list that a certain number of these 

 species occur in the bed known as the Cambridge Greensand among 

 fossils which have been washed out of the Gault. Many of them 

 also occur in the Upper Gault and in the micaceous sandstone of 

 Devizes, but few of them range up to the summit of the Greensand. 

 Some of them, such as Ammonites rhamnonotus and Am. 

 Vraconnensis have not been found anywhere else in the south of 

 England and, as English fossils, were only previously known from 

 the Cambridge Greensand ; Am. Studeri again is only known from 

 near Cambridge and from one bed in the Upper Gault of Folke- 

 stone. 



Most of the fossils which belong to this older fauna are 

 phosphatic casts, and some of the casts have evidently been 

 derived from some older deposit. Some of them have been 

 worn and rolled before being embedded in the sandstone, others 

 are sharp casts, but bear no trace of shell, and have small oysters 

 and Serpulse on their surface. 



Some of the phosphatised fossils, however, especially those 

 which had thick shells, such as Area, Cardita, and Pectunculus, 

 have the shell preserved, but replaced by phosphate of lime. 

 Again, some of the casts have only a thin layer of smooth phos- 

 phate, the interior being apparently a mixture of the phosphate and 

 sand, as if the phosphatisation had in these cases been accomplished 



