Mr. Webster on the Strata lying over the Chalk, 225 



a granular quartz. It has more the appearance of an original for- 

 mation, or peculiar crystallization of siliceous matter analogous to 

 that of sugar, than to a substance composed of the detritus of other 

 rocks. 



Numerous large and loose masses of this rock lie scattered over 

 the surface of the chalk country, particularly in Berkshire and 

 Wiltshire, but a bed or continuous stratum of it has not yet been 

 observed. These stones were much employed by our ancestors 

 in building, and before the ground was cleared for the purposes of 

 agriculture they were much more numerous than at present. The 

 huge erections of Stonehenge, which have so much exercised the 

 conjectures of our antiquaries, are chiefly* composed of it, and 

 the blocks were no doubt found on the spot. 



This granular quartz bears a close resemblance to the siliceous 

 cement of the Hertfordshire pudding-stone, which also is often found 

 in loose masses above the London clay. There appears no ne- 

 cessary connexion between the pebbles of this beautiful conglome- 

 rate and their cement, but the dates of their origins were very 

 different ; the siliceous deposition, when it did not envelope any 

 foreign substance, forming the rock called the grey weathers ; and 

 when it fell among pebbles of any kind, composing a pudding- 

 stone. Accordingly we sometimes find in the grey weathers 

 common chalk flints.* 



* It is not a little singular that some of the smaller upright stones of Stoneheng* 

 consist of a sort of greenstone, and must therefore have been brought from a yerjr 

 great distance, no such rock occurring in the neighbourhood. 



+ Specimens of these collected in the neighbourhood of High W^-combe, by the Hon. 

 Henry Grey Bennett, Pres. G. S. are deposited in the Museum of the Society. 



Vol. II. 2 F 



