THE JURASSIC SYSTEM 419 



Oxfordshire the Inferior Oolite undergoes a great change. South of 

 Oxford, as above stated, there is no Inferior Oolite, its beds having 

 Ix'i'ii destroyed; and near Fawler the base of the Bathonian con- 

 tains small blocks of the older limestones covered with Plicatulse 

 and pierced by lithodomous molluscs. These conditions continue to 

 and beyond Charlbury, but north-west of that place near Chipping 

 Norton the Bathonian rests on a representative of the opalinum 

 zone, consisting of a sandy limestone about 6 feet thick in which 

 Lioceras opalinum, Rhynch. cynocephala, and other fossils occur ; 

 moreover this has a pebbly basement bed resting on the Upper 

 Lias clay. 



This sandy limestone may be regarded as the beginning of the 

 Northampton sandstone, which is found again to the eastward at 

 Steeple Ashton and Worton near Deddington, where it consists of 

 calcareous flagstones and sands with ironstone nodules, the beds 

 being 15 or 16 feet thick. 



East of the Cherwell valley we enter Northampton; where the 

 whole Inferior Oolite passes into an arenaceous facies with very 

 little limestone of any kind, though with a valuable oolitic iron- 

 stone at the base. The lower beds are marine deposits and appear 

 to represent the opalinum and Murchisonce zones, but the higher 

 beds are of estuarine origin. Near Northampton the succession is : 



Feet. 



/"White sands, including a bed with plant remains . 12 to 30 

 Lower | Yellow sandstone and brown sandy limestone or'j 

 Estuarine j ragstone, a variable set of beds, sometimes j- 10 to 30 



i. replaced by white sand as at Spratton ) 



. ( Brown ferruginous sandstone and ironstone, with 



ironstone! Lioceras opalinum, Astarte elegans, Rhynch. 



[ cynocephala, etc 30 to 40 



Average 60 feet 



These beds continue to be the sole representatives of the 

 Inferior Oolite till we reach the valley of the Welland, where 

 the thin end of a lenticular mass of limestone appears above the 

 Lower Estuarine Beds and rapidly thickens northward, Incoming 

 the important formation known as the Lincolnshire limestone, 

 which in South Lines is not less than 150 feet thick. 



At its base in South Lincolnshire are some beds of fissile 

 sandy limestone, which form a passage from the Lower Estuarine 

 Beds ; these contain ferns (Laccopteris polypodioides), with Lucina 

 IVrightii, Gervillia acuta, Trigonia compta, Tr. impressa, Astarte 

 elegans, and Malaptera Bentleyi, but no Ammonites. At Colly- 

 weston (near Stamford) these beds are 12 feet thick, but they thin 

 northward and are hardly distinguishable at Ancaster. 



