Oh. XYIL] 



UPPER GREENSAND. 



331 



niart to Clathraria Lyellii, Mantell, a species common to the ante- 

 cedent Wealden period. 



The Pterodactyl of the Kentish chalk, above allnded to, was of 

 gigantic dimensions, measuring 16 feet 6 inches from tip to tip of its 

 outstretched winffs. Some of its elongated bones were at first mis- 

 taken by able anatomists for those of birds ; of which class no osse- 

 ous remains have as yet been derived from the white chalk, although 



Fossils of the Upper Greensand. 



Fig. 323. 



Fig. 824. 



a. Terebrirostra lyra. } Upper Greensand. 



b. Same, seen in profile, f France. 



Ammonites RTiotomageiisu. 

 Upper Greensand. 



they have been fouud (as will be seen in the annexed figures) in the 

 Upper Greensand. 



Tipper Greensand (A. 4, Table, p. 314). — The lower chalk without 

 flints passes gradually downwards, in the south of England, into an 

 argillaceous limestone, " the chalk marl," already alluded to, in which 

 ammonites and other cephalopoda, so rare in the higher parts of the 

 series, appear. This marly deposit passes in its turn into beds called 

 the Upper Greensand, containing green particles of sand of a chloritic 

 mineral. In parts of Surrey, calcareous matter is largely intermixed, 

 forming a stone called jirestone. In the cliffs of the southern coast 

 of the Isle of "Wight, this upper greensand is 100 feet thick, and con- 

 tains bands of siliceous limestone and calcareous sandstone with no- 

 dules of chert. 



The Upper Greensand is regarded by Mr. Austen and Mr. D. Sharpe 

 as a littoral deposit of the Chalk Ocean, and, therefore, contempora- 

 neous with part of the chalk marl, and even, perhaps, with some part 

 of the white chalk. For as the land went on sinking, and the cretace- 

 ous sea widened its area, white mud and chloritic sand were always 

 forming somewhere, but the line of sea-shore was perpetually varying 

 its position. Hence, though both sand and mud originated simul- 

 taneously, the one near the land, the other far from it, the sands and 

 in every locality where a shore became submerged might constitute 

 the underlying deposit. 



Gault. — The lowest member of the Upper Cretaceous group, 

 usually about 100 feet thick in the S.E. of England, is provincially 

 termed Gault. It consists of a dark blue marl, sometimes intermixed 

 with greensand, Many peculiar forms of cephalopoda, such as the 



