Woods of North-East Kent. 895 
It has already been indicated that, in the districts in' which the investi¬ 
gation has been carried out, a number of soils of different structure and 
composition are found in close proximity. The areas covered by the 
various geological deposits are usually small and interpenetrate to a large 
extent, thus producing a system of great complexity. 
Since this is the case it may be concluded that the absence of any 
species from a certain area is determined by conditions existing in that 
area and not by any defect in its method of distribution. An example 
will help to render this point clear. Mercurialis perennis is entirely ab¬ 
sent from Perry Wood (see Text-figs. 1 and 3 ), but is found abundantly 
in Stocking Wood and in Winding Hill Wood, neither of which is more 
than a mile distant. This species produces abundant seed, and at the 
same time possesses an excellent method of vegetative propagation. Its 
absence from Perry Wood must therefore depend on some edaphic factor 
and not on its inability to reach this area. 
In the majority of cases the limits of the various geological forma¬ 
tions are well marked. With the few exceptions already noted this is 
also the case with the types of vegetation found on these deposits. In 
consequence, in a woodland area extending over several formations the 
changes in the composition of the flora met with in passing from one 
deposit to another are often very striking. The woodland area shown 
in Text-fig. 4 affords excellent examples of these sudden changes. The 
woods on the right-hand side of the figure (towards the south-east) are 
situated on alluvial deposits (brick-earth and gravels), and here the vege¬ 
tation approaches the Tertiary type. The underwood is made up chiefly 
of Chestnut (Castanea saliva ), Hazel, and Ash, while Endymion nutans , 
Primula acaulis , and Adoxa Moschatellina are abundant in the ground 
flora ; Mercurialis perennis is absent. The light flora also closely resem¬ 
bles the Tertiary type. The central part of the wood is situated on the 
Thanet Sand, which here contains a considerable proportion of pebbles. 
The underwood consists of Chestnut, and the ground flora is made up 
almost entirely of Mosses ; Endymion nutans and Adoxa Moschatellina 
are absent. This band of Thanet Sand occupies the crest of a ridge run¬ 
ning in a north-easterly direction and extends for a short distance down 
the slope towards the north-west. Lower down on the slope the wood 
is crossed by a band of Chalk, and here the vegetation is typically of the 
Chalk type. The copse is made up of Hazel, Ash, Euonymus europaeus , 
Cornus sanguine a, and Ligustrum vulgar e y with standard Oak and Beech ; 
Yews are also present. In the ground flora Mercurialis is very abundant, 
Endymion nutans is generally distributed, and Adoxa Moschatellina is 
absent. The line of demarcation between the Thanet Sand and Chalk is 
very sharp and can be determined to within a foot by the distribution of 
Mercurialis perennis. The photograph in PL LXV shows the Thanet 
3 n 2 
