178 GEOLOGY OF THE ISLE OF WIGHT. 



the chalk range is first traversed, and on the 

 southern flank of the hills the firestone, gait, and 

 greensand appear, and the latter extend south- 

 ward several miles, and dip beneath another chain 

 of hills capped with white-chalk strata ; and on the 

 south of this second range, the firestone, gait, 

 and greensand again emerge and contribute to 

 form the picturesque region of the Undercliff. 



The Upper and Lower Chalk. — In pur- 

 suing tlus inquiry, I propose, before conducting 

 the reader to the most interesting localities, to 

 explain more fully the inorganic and organic com- 

 position of the principal deposits of the chalk 

 formation ; and thus afford a general view of the 

 mineral characters and organic remains, of the 

 strata that will come under review, in our excur- 

 sions along the southern coast. 



The superior group of the cretaceous system 

 consists of white limestone disposed in strata, 

 which vary in thickness from a few inches to 

 several feet. In the Upper Chalk there are nume- 

 rous parallel rows of siliceous nodules that occur 

 at irregular distances from each other; and in 

 some places there are sheets of flint (called 

 tabular flint) between the layers of chalk, which 

 extend over considerable areas. The cretaceous 

 strata arc also traversed by vertical and diagonal 



