STRUCTURE OF THE UNDERCLIFF. 241 



extends in a terrace beyond it : some of the fossils 

 peculiar to this deposit (Inoceramus sulcatus, and 

 /. concentrlcus) have been obtained from this place. 

 This bed also appears beneath the firestone on the 

 face of the cliff east of the Sandrock spring, above 

 the road leading to Ventnor. 



The Firestone in the southern face of St. Cathe- 

 rine's hill, above the road from Niton, presents the 

 usual characters of this group as they appear in a 

 succession of terraces along the Undercliff.* The 

 chalk-marl forms the upper part of the series, and 

 passes downwards into greenish grey sands and 

 calcareous strata, in which are layers of bluish 

 marl rock. Strata of cherty sandstone, alternating 

 with layers of sandy marl, occur in the lower part ; 

 and from the disintegration and removal of the 

 intermediate earthy beds, the chert appears in 

 projecting ledges along the face of the southern 

 escarpment of the downs, through a considerable 

 extent of the Undercliff. This circumstance im- 

 parts a peculiar feature to the landscape, and, 

 under certain combinations of rock and vegetation, 



* The firestone strata in the Isle of Wight arc more numerous and 

 diversified than in Kent and the south-east of Sussex, and resemble the equi- 

 valent deposits in the western district of Sussex and Hampshire, so ably 

 elucidated by Sir Roderick Murchison, in his first contribution to that 

 department of natural philosophy, the boundaries of which his genius and 

 important researches have since so largely contributed to extend. (See Geol. 

 Trans, vol. li. Second series. 1826.) 



