VALLEY GRAVELS. 221 



strip of Greensand nearly always intervenes between the gravel 

 and the Alluvium. The greater age which this difference in level 

 indicates, together with the difference in character, justifies the 

 placing of the gravels and the Alluvium in separate group;i. It 

 will be seen also that great changes in the physical geography of 

 the Island have taken place since the gravels were deposited. 



The Valley Gravels are most fully developed in the valleys of 

 the two Yars at the eastern and western ends of the Island 

 respectively. Those of the Medina are comparatively unim- 

 portant. 



The Valley Gravels of the Eastern Yar. 



The longest feeders of this river descend from Whitwell and 

 Niton, and from Wroxall. From near Whitwell northwards an 

 almost continuous terrace of gravel borders the Alluvium on one 

 side or the other. The gravel ranges in thickness up to 10 feet, 

 and is generally loose and stony, but occasionally consists in the 

 upper part of loam. Small pits for road metal may be seen 

 almost everywhere, and a good section occurs at Beacon Alley in 

 a road-cutting. 



The gravel of this part of the valley has doubtless been derived 

 from the Blake Down plateau, and from the continuation of it, 

 which is indicated by the small patches north of Whitwell. The 

 terraces cease at Budbridge, and the streams which descend from 

 Godshill, where there are no Plateau Gravels, are entirely devoid 

 of gravel terraces. 



The Wroxall feeder, on the other hand, draining a country in 

 which outliers of Plateau Gravel form a marked feature, is bor- 

 dered by the most extensive gravel terrace in the Island. The 

 terraces near Sandford are narrow, but the gravel is well seen in 

 several pits. A little further north the valley widens out into a 

 nearly level space a mile broad, and about ]| miles long, uni- 

 formly overspread with gravel, except in the sides of the channels 

 which the river and its tributaries have cut in it. This gravel has 

 been extensively dug at Horringford in a siding from the railway, 

 where the cuttings show well the irregular surface of Lower 

 Greensand on which it rests. 



From Horringford eastwards the terraces occur on the north 

 side of the river only. The gravel appears repeatedly on the top 

 of the bank of Lower Greensand, at a height of only about 6 feet 

 above the Alluvium. 



In the lower part of the Yar there are no terraces, but the 

 tributary which descends from Apse has formed a large gravel flat 

 near Black Pan. The gravel, dug near Ninham, and near the 

 high road to Sandown, contains much chert and greensand, but 

 has no doubt been principally formed from the old Plateau Gravel 

 of which patches still remain on the neighbouring hill-tops, as 

 previously described. 



North of the Downs patches of stony brick-earth at Bembridge, 

 near Howgate Farm, and in the valley south-east of Sea View, 



