WORKING GROUP 3 
JARVIS 
179 
Fig. 1. 
Mainly gro*i 
j [-' ,'d Heath with trees. 
1 [‘‘.' l Parklan<1 
[ | Heath (Light tone 
fMI w«'*"’"* 
; j Heath (Dark tone 
Fig. 2. 
able, the greatest coincidence occurring at the highest and lowest levels - 
bounding the main valley floor and the highest terrace surface. Between these 
areas of good agreement the many slope boundaries vary in their approxima 
tion to soil boundaries. In the north west the steeper bluffs mark an outcrop 
of Ypresian clay, bearing a distinctive soil type, whose boundaries coincide 
well with slope boundaries. The land use boundaries reflect the soils to an even 
smaller extent (fig. 4). Heathland tone differences are unrelated to soils, 
being the result of human interference such as burning. The boundaries of 
farming patterns are the most useful, though they do not agree well with soil 
boundaries. There is a close coincidence between the boundary of the two 
main arable divisions and a soil boundary. 
What are the reasons for these divergences? The chief factor is Pleistocene 
solifluction: by this process, material on certain slopes has moved from higher 
outcrops. Thus, for example, a soil on a Cuisian plateau surface may continue 
down adjacent slopes, although these slopes are due to the presence of an out 
crop of Ypresian clay. Only where there is no solifluction deposit does the soil 
typical of Ypresian clay appear, and such places may not be distinguished by 
a change of slope. Other important soil variations which are not reflected by 
a change in slope occur on a plateau surface: here different soil parent mate-