Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. XVIIL] FOSSILS OF LOWER GREEXSAXD. 34:3 Pebbles of quartzose sandstone, jasper, and flinty slate, together with grains of chlorite and mica, speak plainly of the nature of the Fig. 830. Perna MulUU. Desh. and Leym. a. Exterior. b. Part of hinge of upper valve. preexisting rocks, from the wearing, down of which the Greensand beds were derived. The land, consisting of such rocks, was doubt- less submerged befor
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Ch. XVIIL] FOSSILS OF LOWER GREEXSAXD. 34:3 Pebbles of quartzose sandstone, jasper, and flinty slate, together with grains of chlorite and mica, speak plainly of the nature of the Fig. 830. Perna MulUU. Desh. and Leym. a. Exterior. b. Part of hinge of upper valve. preexisting rocks, from the wearing, down of which the Greensand beds were derived. The land, consisting of such rocks, was doubt- less submerged before the origin of the white chalk, a deposit which originated in a more open sea, and in clearer waters. The fossils of the Lower Cretaceous are for the most part specific- ally distinct from those of the Upper Cretaceous strata. Among the former we often meet with the genus Scaphites or Ancyloceras (fig. 331), which has been aptly described as an ammo- Fig. 331
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