TIIK JURASSIC SYSTEM 417 



Xarnr.s of Beds. Zones. Thickness. 

 Terebratula Beds and Witchellia Grit) 1ir .. , . 



rove freestone jWtoMU*. . . 36 to 55 



iocerasconcavun . 20 to 35 



Freestones and Oolitic marl 1 T , . . lf ,. 



Pea-grit and brown limestone jLudungw Murchwnr. 40 to 160 



Cap of Cephalopoda Bed Lioceras opalinum . 1 to 2 



From 100 to 250 



The Cephalopoda Bed was described on p. 399 as a condensed 

 representative of several zones and forming a "junction bed " 

 between the Toarcian and Bajocian of the Cotteswold district 



Above it there are generally some beds of brown ferruginous 

 limestone, and then comes the " Pea-grit," a coarse pisolitic lime- 

 stone, 4 to 20 feet thick, which extends from Dursley to 

 Nottingham Hill near Winchcombe, a distance of about 30 miles. 



The freestones are soft pale-coloured oolites in thick beds, and 

 are locally separable into lower and upper freestones by a band of 

 yellowish oolitic marl full of Terebrdtula fimbria. 



The beds which form the zone of Lioceras concavum are locally 

 called "grits," but this is a misnomer as they are really rough 

 shelly limestones. The Trigonia Grit is characterised by Trig. 

 costata, T. striata, and T. sculpta, and the Gryphite Grit by GrypJuea 

 sublobata. Other common fossils in these beds are Astarte elegans, 

 A. excavata, Ceromya bajociana, and Pholadomya fidicula. 



The Notgrove freestone occurs only in the northern part of the 

 Cotteswold area, thickening northward from 4 to about 30 

 feet. It and the overlying beds are grouped together by Mr. 

 Buckman, who regards them as occupying a lower horizon than the 

 zone of Stepheoceras Humphriesianum, which appears to be absent 

 in the Cotteswolds. 



Above the beds containing Terebratula Phillipsi there is a 

 marked plane of erosion, the succeeding " Upper Trigonia Grit," 

 or Parkinsoni zone, cutting across all the beds in several directions, 

 but especially eastwards, till it lies directly on the Lias. In the 

 northern part of the Cotteswold area, between the Vale of Winch- 

 combe and Stow-in-the-Wold, the Inferior Oolite has been flexed 

 into a syncline, while the Vale of Moreton to the east coincides 

 with an anticline, the axes of these flexures running approximately 

 north and south. 



These flexures were produced and a plane of erosion cut across 

 them before the deposition of the Bath Oolites, as shown in 

 Fig. 141 which is modified from one drawn by Mr. Buckman. 



Midland Counties. In passing from Gloucestershire into 



2 E 



