30Q 
ELEMENTS OF GEOLOGY. 
The chloritic sand is regarded by many geologists as a 
littoral deposit of the Chalk Ocean, and therefore contempo- 
i*aneous with part of the chalk marl, and eyen, perhaps, with 
some part of the white chalk. For, as the land went on sink¬ 
ing, and the cretaceous sea widened its area, white mud and 
chloritic sand were always forming somewhere, but the line 
of sea-shore was perpetually shifting its position. Hence, 
though both sand and mud originated simultaneously, the 
Fig. 267. 
Ostrea columba. Syn, 
Gryphcea columba. 
Chloritic sand. 
Fig. 268. 
Ostrea carinata. Chalk marl and chloritic sand. 
Neocomian. 
one near the land, the other far from it, the sands in every 
locality where a shore became submerged might constitute 
the underlying deposit. 
Among the characteristic mollusca of the chloritic sand 
may be mentioned Terebrirostra lyra (Fig. 269), Plagiostoma 
Fig.269. 
Terebrirostra lyra, Sow. Pecten ^-costatus. White Plagiostoma Hoperi, Sow. 
Chloritic sand. chalk and chloritic Syn. Lima Hoperi. White 
sand. Neocomian. chalk and chloritic sand. 
Hoperi (Fig. 271), Pecten quinque-costatus (Fig. 270), and 
Ostrea columba (Fig. 267). 
The cephalopoda are abundant, among which 40 species of 
Ammonites are now known, 10 being peculiar to this sub¬ 
division, and the rest common to the beds immediately above 
or below. 
Gault.—The lowest member of the Upper Cretaceous group, 
