Mr. Webster on the Strata lying over the Chalk. 235 



which is not so evident, as they differ in many respects from the 

 chalk flints in their usual state. Of these some are of a deep red 

 colour with a great degree of transparency resembling carnelian : 

 others are of a yellow calcedony often translucent and even botryoidal, 

 and they pass into a kind that is yellow, opake, and of a waxy lustre. 

 Others again appear to be nearly allied to hornstone, and are fre- 

 quently of irregular shapes, which are probably those of the original 

 nodules. 



Another remarkable class of siliceous pebbles is found either 

 mixed with all those above mentioned, or alone, or cemented 

 together into a pudding-stone. These appear to have been origi- 

 nally formed of concentric coats or layers of different colours, 

 which vary in almost every specimen. The colours are for the 

 most part yellow, brown, red, bluish-black, grey, and white : but 

 these run into each other by an infinite number of shades. Others 

 are spotted or clouded with different tints, and have much the 

 appearance of Egyptian pebbles. They take an excellent polish, 

 and are then often extremely beautiful. 



These last appear rather more to resemble agates than chalk 

 flints. They are never found of a large size, seldom exceeding 

 two inches in diameter, and generally are not more than one inch: 

 they are of an oval or flattened form, which appears to have been 

 their original figure, although they have evidently been subjected 

 to a certain degree of attrition. 



All the above mentioned pebbles are sometimes surrounded by 

 crusts ; and it does not appear clear whether these are not some- 

 times original, though perhaps stained by the ochreous substances 

 in which they have been imbedded, or whether they are generally 

 the effect of decomposition. Flint appears to be one of the most 

 unchangeable substances with which we are acquainted. We see 



Vol. II. 2 g 



