36 



oyster shell at the top retains its pearly lustre. Other shells- 

 have only left their impressions or cast. Some of the peb- 

 bles are cracked with the heat, and their interstices filled by 

 calcareous matter. 



The whole forms a calcareous sandstone, with very little 

 variation, and is of a pale brown colour*. The parts being 

 distinct, it forms an instructive specimen, and will serve to 

 explain more obscure ones. 



* Sometimes with a darker tint of yellow, and occasionally of a smoky 

 black, especially where wood is found with it. 



