Distribution in the British Isles 



137 



Diagram showing the relationships of the plant-com- 

 munities of the Formation of Siliceous Soils. 



Woods of Betula tomenlosa or of Quercus sessiliflora 



Swamps 

 .Various stages of scrub 



Swamps 



\ 



Na/rdus grassland 



Molinia grassland 



[jMoorland Formation] 



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 Palseozoio 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 rooks, 

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



Woods of Quercus sessiliflora have been recognised in 

 the Lake District and in North and Central 

 Distribution Wales on Ordovician rocks, in west-central 

 sessUiflorse"" England on siliceous Silurians, in Devon- 

 shire and Cornwall on Upper G-reensand and 

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

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

 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 



