61 



FOSSILS OF THE O'OLITE. 



Fig. 104 Astarte mi'nima. 



Fig. 105. Astarte elegans. 



: the 

 among the echi'noderThs, 



Among other shells, we may cite the Dice' r as arieti'na (Jig. 

 106) ; and among: the echi'noderThs, the cida'ris corona'ta 

 (Jig. 107). 



Fig. 106. Mould and shell of the Dice'ras 

 arieti'na. 



Fig. 107. Cida'ris 

 corona'ta. 



56. UPPER O'OLITE. This group is divided into Kimmeridge 

 clay, and Portland o'olite. Kimmeridge clay, (so named because 

 it is well exhibited at Kimmeridge Bay, and near the village of 

 the same name, in the isle of Purbeck), is of a blue, slaty, or grey- 

 ish yellow colour. Above this is the .Portland stone, which, with 

 alternaticns of compact, marly, sandy or o'olitic limestones, termi- 

 nates the Jura'ssic or o'olitic system. 



57. The organic remains which characterize this group are of 

 the genera ostrea, and ex'ogy'ra of particular species (figs. 108, 

 109), sometimes in great abundance. With a few ammonites, we 

 also find mya (fig. 1.11), Pholadomy'a (fig. 110), and Terebra'tula 

 (fig. 112), which are also equally characteristic. Certain beds 

 of this formation contain Paludi'nee, or Helices, consequently indi- 

 cating that streams of fresh water emptied into the seas of that 

 period. 



56. How is the upper o'olite divided ? What is Kimmeridge clay ? 

 What is found above the Kimmeridge clay? 



57. What fossils are characteristic of the upper o'olite ? 



