IT. BRILL. SHOTOVER. THE DOWNS. 19 



formerly estimated at 599 feet c , but now determined to be only 

 567 feet. Cumnor Hurst, on the opposite side of the Thames, 

 marked by the clump of trees, is about 515 feet; Wytham Hill 

 to the north 539, and Stonesheath to the south, about 535 feet. 

 Farther to the west are the prominent detached hills at Faringdon, 

 505 feet, and the low ridge of Highworth, 442 feet ; Cold Harbour, 

 480 ; and Wotton Basset, 464. The hill of Swindon may be in- 

 cluded in the series, 450 feet. 



The strata in this hilly district may be thus classed : 



Lower green-sand of Faringdon. 

 Iron-sand (Wealden) of Shotover. 

 Purbeck beds (traces of). 

 Portland oolite and sands. 

 Kimmeridge clay. 

 Coralline oolite. 

 Calcareous grit. 

 Oxford clay. 



The valley of the Ock, north of the downs of Berkshire, con- 

 tinuous with that of the Thame, north of the dawns of Oxfordshire 

 and Buckinghamshire., is but feebly separated from the vale of the 

 Upper Thames, by the somewhat broken line of moderate hills 

 described in the last section. These hills however constitute a 

 boundary between two sets of receiving rivers, and serve as me- 

 morials of enormous waste of the surface between the oolitic hills 

 and the chalk downs. 



k p g' g" g'" c e 



Diagram IX. k. Kimmeridge clay. p. Portland rock. g'. Lower green- 



sand, g". Gault. g'". Upper green-sand. c. Chalk. e. Eocene strata. 



It will be shown hereafter that the waste referred to as affecting 

 the surface form was preceded by other operations of the same 

 nature (watery action), which in several parts left no Portland 



c Sections accompanying Mr. Stacpoole's Map. The difference corresponds to a 

 similar error in the estimate of the height of Oxford Valley. ^ 



C 2 



