Oolitic Formations in the vicinity of Minchinhampton. 219 



tinction of many forms of molluscous animals, at no time consti- 

 tuted the estuary of a great river. We search in vain for the 

 relics of air-breathing animals and plants periodically carried 

 down and spread over its floor. The only vegetable remains are 

 fragments of wood which may have floated on the ocean wave to 

 whatever quarter the winds and currents directed them. 



With the great Saurians the case was different ; whether deni- 

 zens of the land, of rivers, or of estuary waters, their remains 

 were entombed in the fine mud which fluviatile waters deposit so 

 copiously. 



We should not expect, nor do we find, a large number of ma- 

 rine shells associated with such deposits ; their paucity is per- 

 fectly compatible with what we know of brackish waters of the 

 recent period, and the small number of marine species which 

 they furnish. Precluded then from displaying this description 

 of fossil treasures, we revert to the less striking remains of mol- 

 luscous animals, and these from their number, their association, 

 their separation into distinct groups and other circumstances 

 repeated at different periods, acquire an interest distinct from 

 that which would attach to them as mere examples of fossil con- 

 chology. To illustrate therefore this portion of the subject the 

 present memoir is chiefly directed, interspersed with notices of 

 such remarkable or characteristic forms as have hitherto been 

 imperfectly described, or which impart to these assemblages their 

 prominent and distinguishing features. 



Commencing with the upper portion of the Great Oolite in 

 our vicinity, we find several beds of hard limestone and bands of 

 marly clay, containing a series of shells representing in dimi- 

 nished numbers the inhabitants of the lower and richer fossi- 

 liferous beds of the formation. Several which do not occur in 

 the lower group I will notice ; these are the little Cardium Beau- 

 monti (Archiac), very abundant, Pholadomya nana (Phillips), 

 Chemnitzia, new species, Bulla Hildesiensis (Roemer), Bulla su- 

 prajurensis (Rcemer), Cardium pes-bovis (Archiac), Cardilla grandis 

 (new species). The other forms which commonly occur are Lu- 

 cina lyrata (Phillips), Lucina rotundata (Rcemer), Ceromya semi- 

 striata (new species), Ceromya excentrica (Isocardia, Rcemer). 

 We have been fortunate enough to succeed in clearing the hinges 

 of the two latter species, and have thus ascertained that they 

 have nothing in common with Isocardia, but belong to the new 

 genus Ceromya of Agassiz. Isocardia concentrica must likewise 

 be placed in the same genus. 



Quitting these beds and descending through sandstones nearly 

 destitute of organic remains, we arrive at the shelly oolite locally 

 termed planking, or upper beds of the Great Oolite building stone, 

 a marine deposit distinguished by the great profusion of its fossil 



