162 
F. E. Fritsch and Winifred M. Parker. 
of about four inches, being followed by grey sand with stones. On 
this gravel-area are large patches of the C U facies that have 
slipped down bodily from above and grow on stretches of soil like 
that on the ridge-top. Some of these patches consist of pure C U, 
while on others Erica cinerea flourishes extensively ; the latter are 
no doubt derived from more open parts of the C U facies, in which 
the Erica had managed to hold its own, and now on an isolated 
patch, removed from competition with the Calluna, exhibits a more 
extensive development. Between these patches there are large 
areas of exposed gravel, the recolonisation of which is very slowly 
proceeding, and a study of the process has proved interesting in 
comparison with the colonisation of the burnt areas on the heath. 
On the gravel everything depends on the success of seedlings. The 
vegetation is at present very open, large areas hearing little or no 
growth. Part of the gravel is being colonised by Molinia, large 
plants of which are very abundant at some points and act as a kind 
of sand-binder (PI. V, fig. 3). At other spots numerous seedlings 
and young plants of Erica cinerea , Calluna and Molinia are found, 
whilst Ulex is relatively much less important (cf. Text-fig. 4). A 
Text-Hg. 4. Chart to show recolonisation on exposed gravel ; April, 1912. 
The cross-hatched area marks a patch of Ulex minor in which three Calluna 
seedlings have developed. M, Molinia ; E, seedlings of Calluna; C with an 
enveloping line, Calluna plants ; G, young grasses (in part Molinia) ; R, seedlings 
of Rumex ; B, a small patch of moss (undetermined). 
considerable number of seedlings of Rumex occur. The seedlings 
of all these forms do not appear to make much progress, and it is 
evident that, except for the Molinia , colonisation goes on very slowly. 
