200 Mr. Webster on the Strata lying over the Chalk. 



The counties of SufFolk and Norfolk have been little explored, aind 

 still present a wide field for research. They will I have no doubt 

 amply reward those members of the Society who have opportunities 

 of examining them. 



I shall now proceed to point out those particulars in which I have 

 observed the marine formation which we have been examining to 

 be analogous to some of the strata in the basin of Paris. 



The plastic clay of the Paris basin is described as sometimes con- 

 sisting of two beds separated by a bed of sand. The lower bed is 

 properly the plastic clay. It is unctuous, tenacious, containing 

 some siliceous but no calcareous matter ; and absolutely refractory in 

 the fire when it has not too great a portion of iron. It varies much 

 in colour, being very white, grey, yellow, grey mixed with red, 

 and almost pure red. This clay is employed, according to its qua- 

 lity, in making coarse or fine pottery and porcelain. 



The corresponding beds of clay in this country agree well with 

 this description. The clays of Dorsetshire are extremely pure, and 

 are much employed in the potteries of Staffordshire and other parts 

 of England. In Alum bay we see clays of all the colours just 

 described. Some of them appear very promising, so much so that 

 the late Mr. Wedgewood had pits opened there ; but although ex- 

 tremely refractory, they were found upon trial not to burn sufficiently 

 white for the purposes required. The deep red clays we have seen 

 are very common in many parts of the country over the chalk. 



No fossil shells have been found in this bed of clay in the French 

 basin, nor in the clay pits of Dorsetshire j nor are there any in the 

 pure clays of Alum bay. 



The uppermost bed of potters' clay in France is sandy, blackish, 

 and contains sometimes fossil shells of the genera cytherea and turri- 

 tella, and the sand is often coloured red or bluish grey. 



