192 



LYELL'S ELEMENTS OF GEOLOGY. 



Origin of the Green-sand 'Formation. 



FOSSILS OF THE GREEN-SAND FORMATION. 



Fig. 166. 

 Fig. 165. 



a. Terebratula lyra. Upper Green-sand. 



b. Same, seen in profile. France. 



Fig. 167. 



Pecten 5 costatus. 



Upper and lower 



green-sand. 



Hamites spiniger (Fitton,) near Folkstone.* 



The fossils of the green-sand are marine, and some of them, 

 like the Pecten quinquecostatus, (Fig. 166.) range through all 

 the members of the series. Several forms of cephalopoda, such 

 as the Hamite, (Fig. 167.) Scaphite, and others distinguish the 

 Green-sand formation in England from the White Chalk. 



Origin of the Green-sand formation. Unlike the white 

 chalk, this deposit consists of a succession of ordinary beds of 

 sand, clay, marl, and impure limestone, the materials of which 

 might result from the wearing down of pre-existing rocks. The 

 nature of these derivative rocks we learn, from finding in the 

 green-sand pebbles of quartz, quartzose sandstone, jasper, and 

 flinty slate, together with grains of chlorite and mica."f" But we 

 naturally inquire, how it could happen that, throughout a large 

 submarine area, there should be formed, first, a set of mechani- 

 cal strata, such as the green-sand, and then over the same space 

 a pure zoophytic and shelly limestone, such as the white chalk. 

 Certain causes, which during the first period gave rise to depo- 



* .Fitton, Geol. Trans;, Second Series, vol. iv. pi. 12. 



t Ibid. p. 116. 



