62 



OOLITIC GROUP. 



as the Kimmeridge, Oxford, and Lias Clays ; these clays 

 generally forming vales throughout their extent, and modi- 

 fying both the agricultui'al character and physical aspect of 

 the different districts. 



The subdivisions, however, of the Oolitic Group, have 

 been subjected to considerable modifications, when traced 

 over the area occupied by them, both as regards their 

 mineral composition and thickness, some beds thinning 

 out and becoming entirely wanting. The labours of Mr. 

 W. Smith, Mr. Lonsdale, Professor J. Phillips, Mr. Cony- 

 beare, and Sir H.T. de la Beche, have contributed materially 

 towards the elucidation of the Oolitic districts, and their 

 works (quoted at the end of this article,) should be 

 consulted for fuU and valuable details of this highly in- 

 teresting portion of English Geology. It has been 

 emphatically called, " The Age of EeptUes," but numerous 

 species of Pish, Corals, Cmstacea, Conchifera, Gas- 

 teropoda, Cephalopoda, especially Ammonites and Belem- 

 nites abounded at this period. The most interesting 

 feature, however, in the organic lustory of this system, is 

 the appearance, for the first time, of warm-blooded animals ; 

 viz., the Amphitherium and Phascolotherium, found in the 

 Stonesfield Slate, and considered, by analogy of structure, 

 to belong to the MarsupiaHa, a family noAv inhabiting the 

 Australian continent. 



The following is a slight account of the mineral cha- 

 racter of the various members of the Oolitic Series, and 

 some of the localities where they are best developed. 



Portland Stone, 

 and Sand. 



Coarse oolitic shelly 

 limestone ; sometimes 

 fine-grainedor compact, 

 thick-bedded, and with 

 layers of chert, and 

 with subordinate beds 

 of sand. 



Isle of Portland. 

 Brill, &c. Aylesbury, 

 Bucks. Thame, Oxon. 

 Tisbury, WUts. 



