Distribution in the British Isles 



137 



Diagram showing the relationships of the 'plant-com- 

 munities of the Formation of Siliceous Soils. 



Woods of Betula tomentosa or of Quercus sessiliflora 



.Various stages of scrub' 



Swamps 



/ 



Swamps 



Molinia grassland 



[Moorland Formation 



Na/rdus grassland 



I Swamps 



Nardus grassland with much Calluna 



B. Other Regions 



The formation of siliceous soils above described appears 

 to be developed on all the siliceous rocks of the Pennine 

 chain; its extension in the British Isles is however far 

 wider than that. So far as they have been investigated the 

 formation appears to be almost co-extensive with the 

 siliceous rocks of Palaeozoic age below a certain altitude ; 

 these, as was pointed out in Part I, occupy a large part 

 of western England, Wales, Scotland and Ireland. Similar 

 woods also occur on some of the harder secondary rocks, 

 e.g. the non-calcareous oolites of north-east Yorkshire. 



Woods of Quercus sessilifiora have been recognised in 

 the Lake District and in North and Central 

 Distribution Wales on Ordovician rocks, in west-central 

 ° '^^^ "^^ England on siliceous Silurians, in Devon- 

 shire and Cornwall on Upper Greensand and 

 on various Palseozoic strata, in Co. Wicklow on Ordovicians, 

 in Co. Kerry on Old Red Sandstone, and in Co. Galway 

 on metamorphic rocks. In Scotland such woods have 

 also been recognised, but their extension has not been 

 studied. In some of the cases mentioned the woods of 



