ERA OF THE OOLITE 



animal, having a foot fifteen inches in length (one-hali 

 more than that of the ostrich,) and a stride of from tour 

 vo six feet, has been appropriately entitled, ornithichnites 

 giganteus. 



ERA OF THE OOLITE. 



COMMENCEMENT OF MAMMALIA. 



The chronicles of this period consist of a series of beds, 

 mostly calcareous, taking their general name (Oolite Sys- 

 tem) from a conspicuous member of them — the oolite — a 

 limestone composed of an aggregation of small round grains 

 or spherules, and so called from its fancied resemblance to 

 a cluster of eggs, or the roe of a fish. This texture oi 

 stone is novel and striking. It is supposed to be of che- 

 mical origin, each spherule being an aggregation of parti- 

 cles round a central nucleus. The oolite system is largely 

 developed in England, France, Westphalia, and North- 

 ern Italy; it appears in Northern India and Africa, and 

 patches of it exist in Scotland, and in the vale of the 

 Mississippi. It may of course be yet discovered in many 

 other parts of the world. 



The series, as shown in the neighborhood of Bath, is 

 (beginning with the lowest) as follows : — 1. Lias, a set or 

 strata, variously composed of limestone, clay, marl, and 

 shale, clay being predominant ; 2. Lower oolitic forma- 

 tion, including, besides the great oolite bed of central 

 England, fullers' earth beds, forest marble, and cornbrash ; 

 3. Middle oolitic formation, composed of two sub-groups, 

 the Oxford clay and coral rag, the latter being a mere 

 layer of the works of the coral polype ; 4. Upper oolitic 

 formation, including what are called Kimmeridge clay 

 and Portland oolite. In Yorkshire, there is an additional 

 group above the lias, and in Sutherlandshire, there is ano- 

 ther group above that again. In the wealds (moorlands) 

 of Kent and Sussex, there is, in like manner, above the 

 fourth of the Bath series, another additional group, to 

 which the name of the Wealden has been given, from ita 

 situation, and which, composed of sandstones and clays, 

 is subdivided into Purbeck beds> Hastings sana and Weald 

 clay 



