RIVERS AND STREAMS. 95 



stood. The northern district, consisting of fresh- 

 water and marine eocene deposits, is marked 

 tertiary. The chalk downs are seen in their full 

 extent from east to west, the dotted lines denoting 

 the inclined direction of the strata as indicated 

 by the layers of flint nodules ; and the lower mem- 

 bers of the cretaceous system occupy the southern 

 portion of the Island ; the principal subdivisions, 

 viz. the firestone (/.), gait (g.), and greensand (g*s.), 

 being marked with letters of reference. The 

 wealden strata (w.) are shown in the bays on the 

 east and west of the Undercliff. The vertical cut 

 or section through jlie island from north to south, 

 explains the position and flexures of the strata, 

 which have given rise to the present geological 

 characters of the surface of the country ; the 

 wealden constituting the foundation and central 

 axis of the Island. 



Rivers and Streams. — There is a good supply 

 of water, at a moderate depth, throughout,, the 

 greater part of the less elevated districts ; but the 

 rivers and streams are neither numerous nor con- 

 siderable. The drainage of the country is chiefly 

 effected by four or five rivers that flow from the 

 northern flanks of the chalk downs. Of these, 

 the principal is the Medina, which, rising at the 

 north-eastern base of St. Catherine's-hill, meanders 



