Association of the Sessile Oak 123 



sandy soils are related to conspicuous differences in the 

 plant-communities which characterise the two kinds of 

 soil respectively. On clayey soils, the characteristic 

 woodland association is dominated by Quercus Bohur, or 

 a mixture of this and Carpinus Betulus ; and such woods 

 on degeneration give rise to neutral grassland. On sandy 

 soils, the woodland associations are more varied in 

 character. Quercus Bobur, Q. sessilifiora, Fagus sylvatica, 

 Betula tomentosa, and Pinus sylvestris may all form more 

 or less definite plant-communities, with many intermediate 

 stages; and these on degeneration give rise to typical 

 heaths often intermingled with grassy patches containing 

 many arenicolous Species. On siliceous soils, the typical 

 woodland association is dominated by Quercus sessilifiora 

 ov, at higher altitudes, by Betula tomentosa; and these 

 on degeneration give rise to a type of grassland which we 

 may call siliceous pasture, whose characteristic, wide- 

 spreadj and dominant species are Nardus striata and 

 Deschampsia flexuosa. 



Association of the sessile oak (Quercetum sessili- 

 florse). Over non-calcareous rocks of the 

 and soil!' Pennine hills in the north of England, 



oakwoods whose dominant tree is Quercus 

 sessilifiora are typically and characteristically developed. 

 The rocks of these hill slopes consist of alternating beds 

 of sandstones and shales belonging to the Pendleside 

 (Yoredale) series, Millstone G-rit, and Coal-measures. 

 In all cases, these soils have a very low lime-content. In 

 several analyses, the percentage of lime (calculated as 

 calcium oxide) was so low as 0"02 per cent.; and in no 

 case was it higher than 0"05 per cent. The total soluble 

 mineral-content of all these soils is also very low. The 

 soils often show a marked tendency to allow of the 

 accumulation of acidic^ humus ; and the amount of such 



1 This word is used by Dr Moss for soil of any kind whose waters 

 give an acid reaction [Editor]. 



