328 



THE GEOLOGIST. 



Section of the Oyster-deposits at Sunderidge. The figures refer to the table of strata at page 327. 



Of the shells which enter into the formation of this conglomerate, the 

 great bulk are oysters, many specimens of which are found with the 

 valves closed, others with them open, whilst multitudes of single valves 

 abound, a few covered with Vermilia and Serpula on both surfaces, and 

 exhibiting also perforations of Clionidse. The interior of most of the 

 closed oysters is occupied by a lining of carbonate of lime, from one to 

 three or four lines in thickness, leaving a central cavity ; the internal 

 surface of which is studded with very small dog-toothed crystals of 

 calcareous spar. This phenomenon I noticed also in many angular 

 cavities in the rock itself, alongside of other imbedded shells. Many of the 

 oysters resembled the common edible species of the present day, whilst 

 others were thick and massive with a large and wide hinge ; some of the 

 latter I measured 5| inches long, and 4| wide. Many specimens were 

 adherent to a single pebble, three or four commonly, and the mass 

 which I have already referred to had six perfect oysters attached to a 

 large pebble, besides about nine different valves of dead specimens 

 adherent to the pebble and to one another. On the upper valve of one 

 of the perfect oysters, four young ones, about half an inch wide, are 

 attached, and quite perfect, a circumstance which especially points 

 to their having grown on the spot. Nevertheless, I would infer that 



