142 NEOZOIC TIME. [CHAP. IX. 



of Lincolnshire, but then becomes thinner, and in York- 

 shire it is only from 100 to 150 feet thick, the lower part 

 (30 to 80 feet) consisting of sandstones and sandy lime- 

 stones (Kellaways Eock). 



The beds known as Coral Eag and Calcareous Grit are a 

 variable set of oolitic and coralline limestones and calca- 

 reous sandstones, which are only developed in the southern 

 counties and in Yorkshire, being absent, or represented by 

 clays with thin layers of limestone, in the counties of 

 Bucks, Beds, Hunts, Cambridge, and Lincoln. At Upware 

 near Ely, however, there are the remains of a small isolated 

 coral-reef, part of the mass consisting of coral-rock, and 

 part of soft coral- sand limestone. 



The Kimeridge Clay consists of dark clays and carbona- 

 ceous shales, which are continuous across England. Theyare 

 thickest in the southern counties, 700 to 800 feet in Dorset, 

 and over 1,000 in the sub-Wealden boring (Sussex). To- 

 ward the Midland counties they become thinner, being only 

 500 at Swindon, and apparently not more than 100 feet at 

 Headington, near Oxford. Northward, however, they 

 thicken again, but cannot be estimated, because of the 

 overlap of the Cretaceous rocks. In Lincolnshire the group 

 is at least 500 feet thick, and is about the same at Speeton 

 in Yorkshire. 



The Portland Beds of Dorset consist in the lower part of 

 calcareous sands and marls (about 80 feet), and in the 

 upper of shelly, chalky, and oolitic limestones (80 to 90 

 feet). A similar succession is found in the Vale of War- 

 dour, but at Swindon the limestones are partly replaced by 

 sands, with large calcareous concretions, and are separated 

 into two stages by a surface of erosion, the uppermost beds 

 being partly marine and partly freshwater, with a Purbeck 

 facies. 1 The lower sands and marls are still 76 feet thick, 



1 See J. F. Blake in " Quart. Journ. Geol. Soc.," vol. xxxvi. p. 203 , 

 and " Historical Gteology," Bohn's Series, p. 348. 



