UPPER FRESH WATER FORMATION. 307 



4. Upper Fresh Water Formation. 

 This formation also occurs in the Isle of Wight, in 

 the hill of Headen, where it rests immediately on the 

 last mentioned, or upper marine formation. It is an ex- 

 tensive calcarious bed, fifty-five feet in thickness, every 

 part of which contains fresh water shells in great abun- 

 dance, without any admixture whatever of marine or- 

 ganic remains. The marl is soft, and easily affected by 

 the weather, but includes a harder variety, which is so 

 durable as to be employed as a building stone. Many 

 of the shells found in this bed are quite entire, and these 

 are intermixed with numerous fragments of the same 

 species. They consist, like the lower fresh water for- 

 mation, of several kinds of lymnei, helices, and planor- 

 bes ; and from the perfect state of preservation in which 

 they are found, appear to have lived in the places where 

 they now are, the shells of these animals being so friable, 

 that they could not have admitted of removal from their 

 native situations without being broken. 



Over this bed is another of clay, eleven feet in thick- 

 ness, containing numerous fragments of a small non-de- 

 script bivalve shell. Upon this lies another bed of yel- 

 low clay without shells, and then a bed of friable calca- 

 rious sandstone, also without shells. To this sandstone 

 succeed other calcarious strata, containing a few fresh 

 water shells. In these are parts of extreme compactness, 

 and other parts contain masses of a loose chalky matter, 

 ?Tiost of which are of a round form; and among these 

 also are many beds of a calcarious matter, extremely 

 dense, and much resembling those incrustations that have 

 been formed by deposition from water on the walls of 

 ancient buildings in Italy. Through all these last strata 

 are veins, ^frequently several inches in thickness, of ra- 



