PHYSICAL CHANGES. 587 



From the time of the Upper Old Red Sandstone onwards to that 

 of the Coal-measures, while the conditions changed from lacustrine 

 to marine, and from marine to estuarine and terrestrial, there 

 were over parts of this area continuous accumulations of strata ; 

 but the close of the Carboniferous period was attended by marked 

 changes, for many of our so-called Coal-basins were then formed, 

 by the crumpling and subsequent denudation of the strata. Dart- 

 moor was uplifted, the Devonian rocks were much folded, while the 

 Culm-measures of Devonshire, more yielding in nature, have been 

 remarkably contorted. The Mendip anticlinal was raised, and its 

 extension through the Steep and Flat Holmes to the Old Red 

 Sandstone and Carboniferous rocks of south Glamorganshire is 

 well marked, although eastwards its prolongation is a matter of 

 speculation, being now concealed by newer strata. The dis- 

 turbances which have culminated in the Pennine escarpment must 

 then have been initiated, and on the whole, what may be termed 

 the ' back bone ' of our country was formed. 



The strata grouped as New Red Sandstone, which were deposited 

 on the folded and eroded surfaces of the older rocks, commenced a 

 new era, and they are the earliest members of that series of strata 

 which, on the whole, lies with marked regularity and in sequence 

 from the western and north-western highlands towards the east and 

 south-east, forming the foundation of the second type of scenery 

 previously mentioned. Parts of Cornwall, Devon, the IMalvern 

 area, Wales, and the Lake District, perhaps also of Charnwood 

 Forest, and of areas in the south-east of England, appeared above 

 water during portions of the Secondary era. The New Red Rocks, 

 Rhoetic Beds, Lias and Oolites were accumulated over this midland 

 and south-eastern area, sometimes overlapping one another, and 

 again occupying more restricted areas. Here and there on the 

 Mendip Hills, and in South Wales, we find the marginal deposits 

 of the Trias, Rhaetic Beds, and Lias, and even of the Inferior 

 Oolite to the east of the Mendips, while some of these deposits, as 

 Sir A. C. Ramsay suggested, may have entirely surrounded the old 

 land of Wales. But the actual extent of most of the later Jurassic 

 strata is in this country a matter of speculation. In Yorkshire we 

 find evidences of the proximity of land more abundant than in the 

 more southerly developments of the Oolitic series. The highest 

 strata (Purbeck) exhibit the incoming of freshwater conditions 

 that prevailed over a more limited area, and were succeeded by 

 the thick freshwater accumulations of the Wealden formation. 

 The physical conditions that attended these strata were followed 

 by partial subsidence, which allowed the sea to encroach over a 

 large area, producing the detrital sediments of the Lower Green- 

 sand ; and these overstep many of the Jurassic strata, which were 

 wasted over a plain of marine denudation. This is in some measure 

 supported by the fact that no old river-valleys are met with on this 

 plain of Jurassic rocks. Later still the marine deposits of Gault 

 and Upper Greensand overspread the Lower Greensand, and con- 

 tinued the plain of marine denudation across the entire Jurassic 

 series, on to and over the New Red rocks of Devonshire, so as in 



