24 SCIENTIFIC SURVEY OF YORK AND DISTRICT 



significant that this moorland area has a lower rainfall than that either to 

 the north or south. 



South of the Aire gap the cottongrass moss is again dominant, and 

 from here to the southern limit of the county the district is composed 

 entirely of rock of the Millstone Grit series and the Coal Measures. In 

 this gritstone area few species occur excepting those of wide distribution, 

 one of the most interesting being Trientalis europcea on Soil Hill on the 

 moors between Halifax and Keighley, its most southern station in Britain. 

 Others of interest are the cloudberry (Rubus Chamcemorus) , forming grey- 

 green patches on the dark cottongrass moss, and the rarer bearberry 

 (Arctostaphylos Uva-ursi). 



Sphagnum bogs are infrequent and of small extent and often bear a 

 network of the slender stems of cranberry [Vaccinum Oxycoccus). On 

 the summit plateau of the Pennines is probably the greatest development 

 known of cottongrass moss. Buried trees are common at the base of the 

 peat, birch, oak, hazel and occasionally pine, which are the remains of the 

 Pennine forest submerged by peat during Atlantic time. Over con- 

 siderable areas retrogression is going on, the peat being completely 

 removed, revealing patches of bare stony ground slowly becoming 

 reinvaded by hair-grass and mat-grass. The better drained slopes are 

 covered by bilberry, crowberry, and grass-heath, with an extensive 

 development of bracken up to the higher springs on the clough sides. 

 Relics of the Birch-Oak-Heath Forest occupy the rock terraces and 

 slopes too steep or stony for cultivation. This type degenerates into 

 the Calluna moor and grass-heath. 



On the Coal Measures at lower levels moist oak woods prevail on the 

 deeper soils over the shales and have a richer ground flora, but the oak- 

 heath type is frequent on the Coal Measure sandstones. Oak is the 

 dominant tree in these woods, but is often replaced by plantations of 

 sycamore, and to a less extent by beech, elm, and pine. In the river 

 valleys are relics of the Alder-Willow thicket. Fringing the moorland 

 is upland pasture, where the dark sandstone walls contrast strongly 

 with the white walls of the calcareous dales. In the Coal Measure 

 area hedgerows are more frequent, especially over the shales, but they 

 usually have a poor flora. Arable land is rare on the foothills and in the 

 dales of the Pennines, the land being largely given up to pasture. 



Cutting off the carboniferous rocks to the east is the Permian ridge 

 or Magnesian Limestone tract which runs through the county from 

 north to south and forms a boundary between the western uplands and 

 the great central Vale of York ; this ridge is cut through by the rivers 

 flowing from the Pennines and in part is covered by drift carried down 

 by former glaciers of the dales. 



This tract provides several contrasts to the dark soils and pastures 

 of the Coal Measures. The rainfall is low and the fertile soil favours 

 a rich and varied vegetation. The reddish soil of the ploughed fields 

 in the spring contrasts with the vivid green of the pastures, and the 

 rich hedgerows have a varied flora both in shrubs and herbaceous species. 

 Little uncultivated land exists in the tract, yet it is one of considerable 

 interest to the botanist. Trees are usually abundant and of fine growth ; 



