Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/184

150 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 7, passed westwards as far as the hilly ground of Devonshire, running out between Wales and Devonshire through what is now the Bristol Channel. The whole of the middle of England was likewise covered by the same deposits, viz. the plains of Shropshire, Cheshire, Lancashire, and the adjoining areas ; so that the Lias and Oolites passed out to what is now the Irish Sea, over and beyond the present estuaries of the Dee and the Mersey, between North Wales and the hilly ground of Lancashire, formed of previously disturbed Carboniferous rocks. In brief, most of the present mountainous and hilly lands of the mainland of Britain were mountainous and hilly then, and even higher than now, considering how much they must since have suffered by denudation.

At this period, south of the Derbyshire hills and through Shropshire and Cheshire, the Lower 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 in the south would then be somewhat as shown in fig. 2 (p. 151).

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 Wealden 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, as shown in fig. 3 (p. 151).

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 unconformity of the Cretaceous rocks on the Oolites and Lias of Lincolnshire and Yorkshire.

At this time the mountains of Wales and other hilly regions formed of Palaeozoic rocks must have been lower than they were during the Oolitic epochs, partly by the effect of long- continued waste, due to atmospheric causes, but probably even more because of gradual and greatly increased submergence during the time that the Chalk was being deposited. I omit any detailed mention of the phenomena connected with the deposition of the freshwater and marine Eocene strata, because at present this subject does not seem essential to my argument.

The Miocene period of old Europe was essentially a continental one. Important disturbances of strata brought this epoch to a close, at all events physically, in what is now the centre of Europe ; and the formations formed in the great freshwater lakes that lay at the bases of the older Alps were, after consolidation, heaved up to form new mountains along the flanks of the ancient range ; and all the length of the Jura, and far beyond to the north-west, was elevated by disturbances of the Jurassic, Cretaceous, and Miocene strata. The broad valley of the lowlands of Switzerland began then to be established, subsequently to be overspread by the large glaciers that deepened the valleys and scooped out the lakes.

One marked effect of this extremely important elevation, after Miocene times, of so much of the centre of Europe was, that the flat