TIIK JURASSIC SYSTKM 425 



ut ni'.n- importance in Oxfordshire. Near Bourton the beds are 

 not more than 30 feet thick. 



The Great Oolite limestone first sets in near Bradford-on-Avon, 

 and rapidly thickens northward till, near Bath and Minchin- 

 hampton, it is from 80 to 100 feet, and includes the well-known 

 freestone which goes by the name of " Bath Oolite." This free- 

 >t <.>:!> is from 10 to 30 feet thick, and occurs between two bands 

 of shelly and oolitic limestone, each from 20 to 40 feet thick. 



The Forest Marble succeeds, and near Bradford and Bath its 

 K-IM- incut bed is a band of bluish-grey clay, which is known as 

 the Bradford clay, but is never more than 10 feet thick. It 

 contains many fossils in a fine state of preservation, and has long 

 been known for the abundance of Apiocrinus Parkinsoni (the 

 pear Encrinite). It also contains Waldheimia digona, Terebratula 

 coarctata, and other fossils which are characteristic of the overlying 

 Forest Marble Beds. The latter are from 60 to 100 feet thick, 

 and consist of alternating limestones and clays. 



The Cornbrash forms a persistent band at the top of the series, 

 but is never more than 15 feet thick. 



Midland Counties. In Oxfordshire the Bathonian has the 

 following composition : 



Feet. 

 Cornbrash and Forest Marble . . . 30 to 35 



Great Oolite limestone 

 Stonesfield Beds and Fuller's Earth 

 Chipping Norton limestone 

 Clypeus and Trigonia Grits 



40 to 50 

 15 to 18 

 12 to 15 

 12 to 20 





The limestones of the Parkinsoni zone do not extend into Bucks, 

 but seem to be cut by the base of the Upper Estuarine Beds, i.e. by 

 the current action which preceded the deposition of those beds 

 presently to be mentioned. 



The Stonesfield Beds into which the Fuller's Earth seems to have 

 passed consist of sandy clays and flaggy sandstones which have 

 yielded a remarkable assemblage of fossils, including the remains of 

 five genera of small mammals two Pterodactyles, three Crocodiles, 

 the Dinosaur Megalosaurus, and the Turtle Protochelys, with a 

 large number of fish and of Mollusca. Among the latter are Nerita 

 costulata, Trigonia impretsa, Gervillia acuta, Modiola imbricata, 

 with Ehynchonella concinna. Besides these are remains of ferns, 

 cycads, and conifers. 



When traced northwards into Northampton the Stonesfield 

 Beds pass into a set of sands and clays which are called the Upper 

 Estuarine Series. In the absence of the Inferior Oolite limestone 

 these beds rest on the estuarine beds of the Northampton Group, 



