218 THE BOOK OF NATURE STUDY 



the whole the map of relief corresponds with the geological map, 

 particularly if the latter is so planned as to bring out the contrast 

 between resistant and non-resistant rocks (compare Figs. 64 

 with 65). 



The oldest rocks, and those which have suffered most from 

 earth-movement, constitute the chief mountain ground of the 

 country. North and South Wales, the Welsh Borders, and 

 the Lake District are our chief examples, made of highly folded, 

 jointed, and cleaved rocks of Cambrian, Ordovician, and Silurian 

 ages. Anglesea and the Scottish Highlands are made of the 

 same or older rocks denuded down more deeply. Our chief hills 

 are of newer rocks, and in this class may be placed first those 

 ranges like the Pennine, the South Welsh Hills, the Mendips, and 

 those of Devon and Cornwall, which result from the denudation 

 of the generally gentle folds of Pennine and Armorican type 

 elevated after the Carboniferous Period (Fig. 28). These are edged 

 or surrounded by the New Red Sandstone Plain, and to the east 

 and south-east of that rises a hill group which might be called 

 the Wolds after their chief heights in the Cotswolds. They are 

 made of Jurassic rocks, whose limestone beds stand out as scarps 

 between their clay vales (Fig. 63). The range reaches its maximum 

 in the Cotswolds and in the " Yorkshire Moors/' Elsewhere 

 it tends to die down, when some of the hard limestones pass 

 into softer clays between Oxford and Lincolnshire. The last great 

 range is that of the Chalk Downs (Figs. 66 and 70), which passes 

 with varying height from Flamborough Head to St. Alban's 

 Head, sometimes with minor ranges and foot hills due to the 

 Lower and Upper Greensands. Owing to the Wealden arch the 

 Downs pass out north-east and south-east from Salisbury 

 " Plain " to the North Downs and the South Downs, each accom- 

 panied by the minor ranges described in a previous chapter. 



Thus the general structure of the entire country is related 

 to the broad tectonic arrangement of its rocks. It remains to 

 note the reaction of the rocks, and the factors which result from 

 them, on the inhabitants living on their surface. In considering 

 this relationship, we must bear in mind not only the composition, 

 position, and association of the rocks themselves, but the outline, 

 slopes, aspects, and soils that result from the action of denudation 



