14 Proceedings. 
these the Greensand. ‘The division of the two northern bands 
is obvious from the slope of the Downs; the southern formations 
are divided by the south slopes of the range of which Leith 
Hill and Hindhead form the most conspicuous points. The 
difference of the Chalk flora from the rest is very marked ; the 
chief plants confined to it are:— Viola hirta (Hairy Violet), 
Hypericum hirsutum (Hairy St. John’s Wort), Hippocrepis 
comosa (Horse-shoe Vetch), Gentiana Amarella (Autumnal 
Gentian), Daphne Laureola (Spurge-laurel), Phytewma orbiculare 
(Rampion), and the various Orchises. 
The Greensand is characterized chiefly by heath and bog 
plants, such as Ornithopus perpusillus (Bird’s-foot), Teesdalia 
nudicaulis, Senecio sylvaticus (Wood Groundsel), Filayo minima 
(Least Cudweed), in its dry parts; Comarum palustre (Marsh 
Cinquefoil), Viola palustris (Marsh Violet), Utricularia minor 
(Lesser Bladderwort), and Bog Asphodel, in its wetter situations. 
The remaining formation, the Wealden Clay, has only a few 
rare flowers peculiar to it, such as Cardamine bulbifera (Coral- 
wort) and @nanthe Phellandrium. 
Before leaving the subject of the geological distribution of 
plants, let us glance at the real relation between them and the 
soil. The difference between soils lies in variation of chemical 
composition, and fineness or coarseness of texture; and it is the 
preference for soil of particular composition and a particular 
texture which determines whether a plant will thrive best on one 
or other of the formations present. If a dry shallow soil of very 
fine grains is most advantageous, or if lime is necessary, the 
plant will be found most plentifully on the chalk; if a coarse- 
grained, loose soil is preferable, the plant will flourish best on the 
sand ; while those needing a damp and fine-grained or stiff soil 
will not be able to get a footing except on the clay. 
We have now seen how two of the chief regulators of distri- 
bution are plant surroundings and variation of soil, and the 
only other important factor which shows itself in small areas 
is the arrangement of river valleys. This is considered of so 
great importance in most counties that it is used to afford a 
scientific division of the land for purposes of reference in the 
OE Oo 
