250 UPPER GREENSAND. [Ch. XYII 



Pkillippi, the anterior teeth of which (see fig. 288 a) are sharp and cut- 

 ting, wliile the posterior or palatal teeth (6) are flat, and analogous to 

 the fossil (fig. 287). 



But we meet with no bones of land animals, nor any terrestrial or 

 fluviatile shells, nor any plants, except sea-weeds, and here and there a 

 piece of di-ift wood. All the appearances concur in leading lis to con- 

 clude that the white chalk was the product of an open sea of considerable 

 depth. 



The existence of turtles and oviparous saurians, and of a Pterodactyl or 

 winged lizard, found in the white chalk of Maidstone, imphes, no doubt, 

 some neighboring land ; but a few small islets in mid-ocean, like x\scen- 

 sion, formerly so much frequented by migratory droves of turtle, might 

 perhaps have afforded the required retreat where these creatures laid their 

 eggs in the- sand, or fi-om which the flying species may have been blown 

 out to sea. Of the vegetation of such islands we have scarcely any in- 

 dication, but it consisted partly of cycadeous plants ; for a fragment of 

 one of these was found by Capt. Ibbetson in the chalk marl of the Isle of 

 Wight, and is referred by A. Brongniart to Clathraria Lyellii^ Mantell, a 

 species common to the antecedent Wealdeu period. 



The Pterodactyl of the Kentish chalk, above alluded to, was of gigantic 

 dimensions, measuring 16 feet inches from tip to tip of its outstretched 

 wings. Some of its elongated bones were at first mistaken by able anat- 

 omists for those of birds ; of which class no osseous remains seem as yet 

 to have been derived from the chalk, or indeed from any secondary or 

 piimary formation, except perhaps the Wealden. 



Upper greensand (Table, p. 105, &c.) — 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 

 firestone. In the cliffB of the southern coast of the Isle of Wight, this 

 upper greensand is 100 feet thick, and contains bands of siliceous lime- 

 stone and calcareous sandstone with nodules of chert. 



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

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

 ous 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 simultane- 

 ously, the one near the land, the other far from it, the sands in every 

 locality where a shore became submerged, might constitute the under- 

 lying deposit. 



Gault. — The lowest member of the upper Cretaceous group, usually 

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



