506 Cretaceous Overlap. 



which lie between North Wales and the hilly ground of 

 Lancashire, formed of previously disturbed Carboni- 

 ferous rocks. In brief, most of the present mountainous 

 and hilly lands of the mainland of Britain were moun- 

 tainous and hilly then, and must have been much 

 higher than now, considering how much they have 

 since suffered by denudation. 



At this period, south of the Derbyshire hills, and 

 through Shropshire and Cheshire, the Secondary rocks 

 lay somewhat flatly ; while in the more southern and 

 eastern areas they were tilted up to the west, so as to 

 give them a low eastern dip. The general arrangement 

 of the strata would then be somewhat as in fig. 100. 



The submersion of this low lying area brought the 

 deposition of the Wealden strata to a close, and the 

 Cretaceous formations were deposited above the Weal- 

 den and Oolitic strata, so that a great unconformable 

 overlap of Cretaceous strata took place across the 

 successive outcrops of the Oolitic and older Secondary 

 formations. (See fig. 101.) 



The same kind of overlapping of the Cretaceous on 

 the Oolitic formations, took place at the same time in 

 the country north and south of the present estuary of 

 the Humber, the proof of which is well seen in the un- 

 conformity of the Cretaceous rocks on part of the Oolites 

 and Lias of Lincolnshire and Yorkshire. 



At this time, the mountains of Wales, and other 

 hilly regions made of Palaeozoic rocks, must have beeo 

 lower than they were during the Oolitic epochs'; partly 

 by the effect of long-continued waste due to atmo- 

 spheric causes, but much more because of gradual and 

 greatly increased submergence during the time that the 

 Chalk was being deposited. It is even possible that 



