52 EXPLOITATION OF PLANTS 
_ Thus Moss found that in the Peak District there was 
a sharp distinction between the areas occupied by the 
common and durmast oaks. There the common oak 
is met with growing on deep, non-calcareous, fluvio- 
glacial sands, whilst the durmast oak is restricted to 
the shallow soils overlying the siliceous rocks. The 
same investigator found the common oak forming wood- 
lands in Somerset on the deep sands of the greensand 
-- series, and on the deep calcareous marls. Adamson 
in Cambridgeshire found the common oak both on 
calcareous marl and loam. 
In Hertfordshire the common oak is entirely con- 
fined to the stiff clays and heavier loams, whilst the 
durmast oak is restricted to the lighter loams and 
sands or soils deficient in lime. 
In upland districts the durmast oak forms extensive 
woods on the shallow soils overlying the non-calcareous 
and sometimes calcareous rocks of the steep valley 
sides. 
Thus we find woods of Q. sessiliflora on the lower 
estuarine sandstones of the superior oolite of Yorkshire, 
on the Devonian sandstones of Somerset, and on the 
Cambrian and Silurian rocks of Wales, such woods 
often extending to an altitude of 1000 feet. 
Although we are far from having entirely solved the 
problem of the respective habitats of the two species, 
it is clear that the vague statements of foresters in 
the past have not merely been misleading, but often 
positively erroneous. 
Thus it is evident that except in districts where the 
rainfall is exceptionally high, the durmast oak does 
not naturally occur on calcareous soils, whilst the 
