186 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
Soil formed from 
décalcification of till 
Ridge of till, 
troughs of sandy soil 
Chalky till 
Chalk in situ 
Fig. 3. Contortions in Chalky Till, Garboldisham, Norfolk 
of heather (Calluna vulgaris) and grassland (dominated by Agrostis and Festuca 
spp.). Subsequent work has now shown that in the latter case the heather was 
rooted mainly in the deep, acid, sandy soil in the troughs while the grasses 
were growing over the chalk-rich ridges. Careful field examination has reveal 
ed many other cases where the vegetational differences were less spectacular 
but still easily mapped. 
Since 1946, aerial photography, both vertical and oblique, has shown that 
the patterns are far more numerous and widespread than was at first suspected. 
Patterns of slight differences in soil colour, subtle changes in vegetation and 
small differences in crop performance, none of which are easily seen on the 
ground, are often readily identified. Exceptionally, patterns have even been 
detected by variation in the rate of melting of a thin cover of snow.