154 
CHAP. VII. 
3. CHALK MARL. 
This deposit constitutes tlie foundation of the 
chalk hills, its outcrop forming a fillet or zone 
round theu' base, and connecting the detached 
parts of the range with each other. 
The marl is commonly soft and friable, but indu- 
rated blocks occur which possess the hardness of 
limestone. It is of a light grey colour, inclining to 
brown, and frequently possesses a ferruginous tinge 
derived from oxide of iron. It consists principally 
of carbonate of lime and alumine, with an intermix- 
ture of silica, a very small proportion of iron, and 
perhaps of oxide of manganese. 
Where denuded, the surface of this deposit com- 
poses a fertile tract of arable land, including some 
of the best farms in the country. 
In the range of low cliffs near Southbourn, tlie 
grey marl is seen rising from beneath the chalk, 
and reposing on the firestone, with which it is inter- 
mingled at the line of junction. Its separation from 
the superincumbent bed of chalk without flints is 
well defined, and may be traced with but little diffi- 
culty. From this spot it extends, witli scarcely any 
interru])tion, to Shoreham river, its outcrop being 
interposed between the foot of the Downs and tlie 
basseting edge of tlie gait. 
