Woods of North-East Kent. 897 
north-west the alluvial deposit carries vegetation closely allied to that found 
on the Chalk. 
The woodland area just described is of small extent, and the distance 
across the whole of the different deposits does not exceed half a mile. In 
a case of this kind it is obvious that the composition of the flora depends 
on edaphic conditions and is not affected by difficulties connected with the 
distribution of the species. 
The sudden disappearance of Mercurialis perennis in passing from the 
Chalk to the Thanet Sand has also been observed in the eastern part 
of Joy den’s Wood, near Swanley. In this case a similar change takes place 
in the flora to that just described, but here the line of demarcation is not 
quite so sharply defined. 
Reference has already been made to the constant occurrence of Yew on 
the Chalk. Its restriction to this soil is well exemplified by a consideration 
of its distribution in the woods shown in Text-fig. 2. Each of these woods 
is situated partly on the Chalk and partly on the Clay with Flints. Yews 
are found in the southern part of Badgin Wood (PL LXIV), the south-west 
portion of Rice Wood, and in the north-west corner of Foxburrow Wood, 
but do not occur on any part of the Clay with Flints. Another point 
of interest in connexion with the distribution of species in Badgin Wood is 
the occurrence of Adoxa Moschatellina on the very small area of alluvium 
found in the south-west corner of the wood, this plant being absent from 
the surrounding Chalk soil. 
The changes in vegetation met with in passing from one Tertiary 
formation to another, although not quite so striking as those just described, 
are still well marked. Perry Wood, near Faversham (Text-figs. 1 and 3), 
covers almost the whole of a Tertiary outlier which is made up of Thanet 
Sand, the Woolwich and Reading series, and the Oldhaven beds. The 
presence of this outlier on the Chalk gives rise to a hill reaching 500 feet in 
altitude. The outer and lower parts of the wood on the Thanet Sand con¬ 
sist chiefly of Chestnut coppice, and the flora is similar to that already 
described on the more stony soils of this deposit. On passing to the 
Woolwich and Reading beds the Chestnut is partly replaced by Oak ; 
Endymion nutans. Primula acaulis } Adoxa Moschatellina, and other species 
abundant on the Thanet Sand decrease greatly in quantity or disappear. 
The central and highest parts of the wood exhibit the Oak-Birch-Heath 
type of vegetation, and here Pinus sylvestris has been extensively planted ; 
Pteris aquilina is particularly abundant, although only found sparingly in 
the lower parts of the wood. Farningham Wood, near Swanley, is situated 
on a similar outlier, and here the distribution of the vegetation is almost 
identical. 
In view of the great resemblance of the soils of the London Clay and 
Clay with Flints in both mechanical and chemical composition, a comparison 
