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



up this stratum, of reducing it to fragments, and of disintegrating 

 it, by removing the matrix containing the siliceous matter. And 

 3d. the deposition, either partial or general, of a solution of 

 siliceous earth capable of cementing the whole together into one 

 mass. 



This formation is no doubt of ancient date, and long anterior to 

 that of the present surface of the earth ; a circumstance which is 

 rendered probable by our finding masses of this pudding-stone 

 itself water-worn, indicating, that since its cementation it has been 

 subjected to some of these revolutionary processes, of which we 

 have seen so many other proofs. 



That all the ancient pebbles were not cemented together in a 

 similar manner, is shewn by those in Alum bay, which are in 

 loose sand ; and by those which are found in the beds of sand in 

 the blue clay, both in the neighbourhood of London and at Ports- 

 mouth. 



But that some of the gravel may have been at a former period 

 in the state of pudding-stone, and may have been disintegrated, is 

 a circumstance also highly probable. Yet there does not appear 

 any necessity for supposing that all our gravel has been originally 

 pudding-stone, any more than that all sand has been sand-stone. 



Another species of pebble which is very common, is a striped 

 flint, or rather a kind of hornstone. These appear never to have had 

 crusts, but owe their rounded forms entirely to the action of water. 

 They may be supposed to have been derived from a bed of such a 

 substance, which has been reduced to fragments. Beds of a striped 

 chert very analogous to this I have seen in the island of Portland, 

 alternating with the oolite. 



'Turf^ so abundant in the north of France, is much less frequently 

 seen in this part of England. The practice of draining, and the 



