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



§ 5. Upper Freshwater Formation, 



I have now to describe the most remarkable and best charac- 

 terized of all the strata in that hill in the Isle of Wight called 

 Headen, which has so frequently come under our examination. 



Here, immediately over the last-mentioned formation, there is a 

 thin bed of sand of 6 inches, upon which rests immediately a 

 very extensive calcareous stratum 55 feet in thickness, every part 

 of which contains freshwater shells in great abundance, without 

 any admixture whatever of marine exuviae. 



The substance of which this stratum consists is of various cha- 

 racter, although it cannot be described as being subdivided into 

 smaller beds. A great part is composed of a yellowish white marl, 

 sufficiently indurated to remain in blocks when fallen down, but 

 extremely friable, and which, like other marls, will not endure 

 the frost. In this, and disposed without any regularity, are hard 

 masses of a rock which appears to contain a greater proportion of 

 calcareous matter ; and to be in about an equal quantity with the 

 marl. This stone is very durable, and is employed as a building 

 material. Between these two extremes there are many parts of 

 intermediate degrees of hardness and durability. 



Many of the shells which are found imbedded in this stratum 

 are quite entire, and these are mixed with numerous fragments of 

 the same species. They consist, like the lower freshwater forma- 

 tion, of several kinds of lymnei, helices, and planorbes, and from 

 the perfect state of preservation in which they are found, must 

 evidently have lived in the very spots where they now are, the 

 shells of these animals being so friable that they could not have 



