412 



SPECIAL GEOLOGY. 



The oolitic group is well developed in France, and is 

 divided, by Alcide D'Orbigny, into ten stages. From the 

 entire Jurassic series, this distinguished palaeontologist has 

 collected, for the illustration of his "Paleontologie Fra^aise," 

 3,785 species of fossil mollusca and radiata. The mode of 

 their distribution is shown in the subjoined table, which 

 exhibits the numerical value of the species that characterise 

 each stage : 



Our limits restrict us to a few very general remarks on 

 the fossils of this group. From the table of the distribution 

 of Mollusca and JBadiata in the French Jurassic series we 

 observe that certain stages, as the Corallian and the Ox- 

 fordian, contain a much greater numerical proportion of 

 corals and echinoderms than others ; and the same fact has 

 been observed in the English series. In the Portland beds, 

 corals are rare, whilst one of the limestones of the middle 

 oolite has received the name of coral rag, because it con- 

 sists, for the most part, of zoophytic debris ; many of the 

 corals retaining the position in which they grew at the bed 

 of the ancient sea.* 



At Steeple Ashton are found A8trea,Agaricia, Caryopliyllia, 

 and Explanaria, and other genera, in great abundance and 

 perfection. Similar coralline beds extend through Berkshire 

 and Wilts, and occur likewise in Yorkshire. Many beautiful 



* For lists of fossils of the oolitic, and other groups, we refer the student to 

 the accurate catalogue of British fossils, by John Morris, Esq., a work of much 

 research and great value. Very complete lists are contained in Mr. Tennant's 

 book before cited. 



