10 HILLS AND VALES. CHAP. 



great exhibition of old red sandstone ; while mesozoic strata of 

 great interest and variety fill all the middle space, and tertiary 

 deposits appear on the southern border. I know of no district of 

 equal area which offers so great a variety of interesting facts to the 

 geological observer, in a country as full of natural beauty and 

 historical associations. 



Regarding first the district which includes the drainage of the 

 Thames, and the immediately adjacent region, we find the country 

 marked by ranges of hills, some being formed in almost con- 

 tinuous ridges, others broken into groups of associated heights. 

 These ranges are separated by broad, far-extended vales, a common 

 feature of the more regularly stratified parts of England. In these 

 vales run, with a gentle current, rivers receiving the small streams 

 which descend on either side with greater rapidity. The receiving 

 rivers run more or less parallel to the main ranges of hills, which 

 present escarpments overlooking the vales from the south and east, 

 but on the north and west rise with more gentle and prolonged 

 acclivities. From one of these vales to the next, the collected river 

 runs through a contracted valley, excavated across the dividing 

 ridge ; and it is observed in these, as in other cases in England, 

 that at some point above the contracted passage the country has 

 the aspect of a drained ancient lake ; as if in fact the passage had 

 been forced by a large body of water which had been gathered 

 above. Not unfrequently indeed the appearance of a lake is re- 

 newed by occasional floods of the river. Thus above the contraction 

 in the Thames valley at Iffley and Sandford, spread from time 

 to time the broad waters about Oxford; and, to take a smaller 

 example, Ottmoor, an extensive flat on the river Ray, is not seldom 

 flooded on a great scale above the contraction of the valley at 

 Islip. 



Extending our view from the western terrace edge of the 

 Cotswolds, over the broad and fertile plain, watered by the 

 Avon and the Severn, the Malvern hills rise before us with 

 entirely different forms, and stand as the sentinels of another 

 country. Taking these as the true boundary of our geological 

 field, we have the succession of hills and vales represented on the 

 opposite page. 



Viewed in profile, or as represented on p. 1 1 in section, four ridges 

 and hollows appear, parallel to the ranges of outcropping strata, 



