Dr. BURGER on the Geology of some Parts 



VI. Oviform Limestone (OoUthe). 



I have observed two beds or strata of this roclc: one Is In the 

 quarry of Wind Spit in the Isle of Purbeck. This quarry is open in 

 two places. To the east, where the rock has been excavated on a 

 very large scale, there is nothing but the coarse shelly limestone 

 before mentioned, which as it extends to the western quarry, passes 

 into oviform limestone. The grain of the rock quarried at this latter 

 place, is more close, the colour uniformly white, the texture less 

 coherent ; it still however retains some fragments of shells, but 

 they are small and broken. I found the specific gravity of one 

 specimen 2,539. 



The quarry to the north-west of the Isle of Portland, which is 

 the most extensive, is composed almost entirely of the oviform 

 limestone, containing but veiy few shells ; the texture of the work 

 is granular, the nodules very small, and united by a calcareous 

 cement. It crumbles to pieces much more readily than the coarse 

 shelly limestone which lies on the opposite coast of the island. 

 The specific gravity of one specimen I found 2,464 ; thus giving 

 for the mean specific gravity of the two specimens here mentioned 

 2,5015. 



" Les oolithes," says M. Brongniart, " se trouvent en bancs ou 

 *' en masses considerables au pied des coUines ou des montagnes, 

 ** dans le passage des terrains de cristallisation, aux terrains de sedi- 

 " ment : elles sont rares dans la chaux carbonatee compacte : on-ne les 

 " a jamais vues dans la craie proprement dite ; il paroit qu'elles sont 

 " particulieres a la chaux carbonatee grossiere."* 



* Traite element, de Mineral, tome i. p. 203. 



