CHAP. VII.] DYASSIC PERIOD. 103 



above are 450 feet thick, and the highest beds (proved in 

 the borings at Middlesbrough) include deposits of rock- 

 salt and gypsum. 



In South Yorkshire the main mass of limestone is 270 

 feet thick, and there are marls and limestones above to a 

 thickness of 140 feet ; but in Notts all the beds are greatly 

 attenuated, the total thickness near Mansfield being pro- 

 bably about 200 feet, of which not more than 100 are 

 limestone, and parts of this are really calciferous sand- 

 stones. Near Nottingham it is still less, and seems to be 

 on the point of thinning out when it is overlapped by the 

 Trias. 



A boring near Newark and about fifteen miles east of 

 the outcrop at Mansfield is important as throwing much 

 light on the lithological changes of the formation. This 

 section proves that while the limestones remain about the 

 same, the formation thickens eastward by an increase of 

 the marls and shales, the calcareous marls at the base 

 having a thickness of 118 feet, as compared with fifteen 

 or thirty feet in Notts. A boring through the Trias at Ow- 

 thorpe, in the south of Notts, proved the Dyas to be want- 

 ing there, and passed directly into Coal-measures. These 

 facts show that, in Notts at any rate, the Dyas thins 

 rapidly both southward and westward, whence we may 

 conclude that land lay in both these directions, an infe- 

 rence which is confirmed by the collection of pebbles found 

 in the basal breccia, which comprises not only pebbles of 

 Carboniferous limestone and fragments of sandstone and 

 shale from the underlying Coal-measures, but pebbles of 

 slate, quartz, and quartzite, which have probably been 

 derived from the rocks of Charnwood Forest. 



B. Passing now to the western districts, we may select 

 that of the Cumberland Plain or Vale of Eden as the 

 most complete and important. Here and elsewhere on the 

 west side of the Pennine chain there is very little lime- 



