44 VEGETATION OF THE PEAK DISTRICT [CH. 



The woods of Quercus sessiliflora and of Betula pubescens 

 are confined to the sandstones and shales. The soil over the 

 sandstones is shallow, that is, shallower than would appear to 

 be necessary for the free growth of the tap roots of Quercus 

 Robur ; and similarly the soil of the shales is frequently shallow, 

 being often interrupted by bands of flagstone and half-formed 

 sandstone. The restriction of woods of Quercus sessiliflora to 

 shallow, siliceous soils is very general throughout the whole of 

 the British Isles; but exceptional cases occur on sandy and 

 gravelly soils in the south-east of England. 



3. The altitude of the woodland site. Woods of 

 Quercus sessiliflora cease at altitudes of about 1000 feet (305 m.), 

 whilst woods of Betula pubescens reach altitudes of about 

 1250 feet (381 m.). As the physical and chemical conditions 

 of the soils of the two associations are identical, it seems 

 clear that the failure of the oak woods to reach the higher 

 altitude is due to the severer climatic conditions which prevail 

 there. Such conditions are the lower temperatures, the greater 

 velocity of the wind, and (to some extent) the lower atmo- 

 spheric humidity and higher rainfall. 



OAK WOODS OF QUERCUS ROBUR 



In this district, woods of the peduncled oak (Quercus Robur) 

 occur only on the western boundary; and they represent the 

 eastern fringe of the lowland oak woods of the Cheshire plain. 

 The latter, in their turn, are a north-western continuation of 

 the lowland oak woods which are characteristic of the Midlands 

 and of the south of England ; and an eastern extension of the 

 latter may be traced through Nottinghamshire and into east 

 Yorkshire. As already indicated, oak woods of Quercus Robur 

 may occur either on deep clays or on deep sands or gravels. 

 Woods of both these types occur on the Cheshire plain, though 

 the oak woods of the sandy and gravelly soils are there more 

 extensive than those on clayey soils. It is the woods of the 

 former type that just reach the western margin of this district. 



The best examples of woods of Quercus Robur in this 

 district occur in the lower courses of the rivers Etherow and 

 Goyt, two of the head-streams of the river Mersey. Ernocroft 

 Wood and Bottoms Hall Wood are examples of such woods, 



