138 NEOZOIC TIME. [CHAP. IX. 



30 feet of strata, in which beds of Lower, Middle, and 

 Upper Lias can be distinguished. This is the case near 

 Badstock, and it is quite possible that the Mendip ridge 

 then extended much further eastward than it does now. 



In Gloucestershire the total thickness of the Lias is little 

 short of 1,000 feet, but at Burford in Oxfordshire it is only 

 650, the difference being due to the thinning of the Middle 

 and Upper members. The formation probably continues 

 to become thinner toward the east, but its limits in that 

 direction are not yet known. 



Middle Jurassic Series. Between the Upper Lias clays 

 and the limestones of the Inferior Oolite there are in the 

 south-west of England certain sands which are grouped by 

 some with the Lias and by others with the Oolite, but they 

 are, in fact, passage beds from one series to the other. 

 Above them come a variable series of limestones and marls, 

 the former generally oolitic, and containing an abundance 

 of fossils. These beds are divided into two groups the 

 Inferior Oolite and the Great Oolite and in the south-west 

 of England they are entirely of marine origin. 



In Dorsetshire their combined thickness is over 700 feet, 

 but they thin northward toward the Mendips, and near 

 Erome they are not more than 100 feet thick. Here the 

 Inferior Oolite overlaps the Lias, and rests on the older 

 rocks, its base being sometimes conglomeratic. 



North of the Mendips they thicken again, and reach a 

 total of 460 feet near Cheltenham; but when followed 

 eastward, they are found to thin very rapidly, the whole of 

 the Inferior Oolite being represented in the valley of the 

 Cherwell by 10 or 12 feet of brown sandstone, and the 

 Great Oolites above are not more than 150 feet thick. 

 There is at the same time evidence of the vicinity of land in 

 this direction, not only from the sandy character of the In- 

 ferior Oolite, but from a thin zone of estuarine beds at the 

 base of the Great Oolite. These are known as the Stones- 



