ALLUVfAL FORMATIONS. 309 



The alluvial deposites in the south of England also 

 contain fossil bones of quadrupeds; and these, according 

 to Mr. Webster, are of different dates. * The most an- 

 cient are entirely petrified, and where found in gravel, 

 are conjectured to have been washed out of the strata in 

 which they were originally imbedded. Of this kind are 

 probably remains of the mastodon, mentioned by Mr. 

 Parkinson. The next class contains the bones of the 

 elephant, rhinoceros, hippopotamus, and the Irish elk, 

 which are frequently accompanied with marl, and fresh 

 water shells. They are, however, not petrified ; and 

 though generally in a state of decay, yet are sometimes 

 quite perfect. They are particularly abundant in Suffolk 

 and Norfolk, but have also been found at Brentford, in 



found either mixed with the flints, calcedonies, and hornstones, or 

 alone, or cemented into a pudding stone. These, according to Mr. 

 Webster, appear to have been originally 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, 

 gray, 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 ex- 

 cellent polish, and are then often extremely beautiful. These last ap- 

 pear rather more to resemble agates than chalk flints. They are never 

 found of large size, seldom exceeding two inches in diameter, and ge- 

 nerally 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. The 

 well known pudding stone of Hertfordshire is composed of these con- 

 centric pebbles, imbedded in a basis of granular quartz. These con- 

 centric pebbles, like the imbedded masses of flint in chalk, of agate in 

 trap, and of felspar in porphyry, are to be viewed as having been 

 formed at the same time with the rock in which they were formerly 

 included. 



* It is still uncertain whether or not all the substances named allu- 

 Fial, are strictly of this nature. The geognostic relations of many al- 

 luvial alleged Deposites are still but imperfectly known. 



