38 GEOLOGY OF THE ISLE OF WIGHT 



the country about Selborne in Hampshire.* But, 

 though the Upper Greensand covers a less area in the 

 Isle of Wight than the Lower, it forms some of the most 

 characteristic scenery of the Island. One of the most 

 striking features of the Island is the Undercliff, the 

 undulating wooded country from Bonchurch to Niton, 

 above the sea cliff, but under a second cliff, a vertical 

 wall which shelters it to the North. This wall of cliff 

 consists of Upper Greensand. In a similar way to the 

 small undercliffs we saw at Luccombe, the Undercliff has 

 been formed by a series of great slips, caused here by the 

 flowing out of the Gault clay, which runs in a nearly 

 horizontal band through the base of all the Southern 

 Downs of the Island, the Upper Greensand lying above 

 it breaking off in masses, and leaving vertical walls of 

 cliff. These walls are seen not only in the Undercliff, but 

 also on the northern side of the downs, where they form 

 the inland cliff overhanging a pretty belt of woodland 

 from Shanklin to Cook's Castle, and again forming Gat 

 Cliff above Appuldurcombe. We have records of great 

 landslips at the two ends of the Undercliff, near Bon- 

 church and at Rocken End, about a century ago. But 

 the greater part of the Undercliff was formed by landslips 

 in very ancient times, before recorded history in this 

 Island began. The outcrop of the Gault is marked by a 

 line of springs on all sides of the Southern Downs. The 

 strata above, Chalk and Upper Greensand, are porous 

 and absorb the rainfall, which permeates through till it 

 reaches the Gault Clay, which throws it out of the hill 

 side in springs, some of which furnish a water supply for 

 the surrounding towns and villages. 



Where the Upper Greensand is best developed, above 

 the Undercliff, the passage beds are followed by 30 feet 

 of yellow micaceous sands, with layers of nodules of a 

 bluish-grey siliceous limestone known as Rag. The 



* Naijies proposed by the late A. J. Jukes-Browne, 



