YORKSHIRE PLANT ECOLOGY 27 



and along the hillside to Roulston Scar : TrolUus europceus, Draba 

 inflata, Viola lutea, Stellaria nemorimi. Geranium sanguineum, Lathrcea 

 squamaria, Primula farinosa, Trientalis europaa, Gagea lutea, Acorus 

 calamus, Lycopodium selagittoides and Ptlularia globulifera. 



The Vale of York is a low-lying, richly cultivated tract extending from 

 the Tees to the Trent and covered by thick beds of alluvial muds, silts, 

 and glacial deposits of gravels, sands and clay. Formerly a wet, marshy 

 area, drainage and enclosure have taken place from 1670 onwards, and 

 now the greater part of it is highly cultivated. Small areas, however, 

 still retain a primitive vegetation. Strensall is the site of a military 

 camp, for which it has been greatly modified, with the loss of many 

 interesting plants. Askham Bog, two miles from York, is perhaps the 

 most primitive area, and preserves the conditions which formerly pre- 

 vailed over a wide area of the Vale of York. Here the drainage is held 

 up by two minor loops of the York moraine and has never established 

 a proper drainage system. The bog and adjoining brick ponds have a 

 rich marsh and aquatic flora, which was described by the Rev. W. C. Hey 

 as consisting of ' pools bordered by flags, sedges, bulrushes and marsh 

 ferns, jungles of Osmunda, with birch, willow and blackthorn. The 

 Bog "is a tangled mass of flags and sweet gale and various low-growing 

 trees.' Since then some of the ferns have been almost exterminated. 



The Chalk Wolds form a crescentic ridge of hills rising to 800 ft., 

 running north from the Humber to Grimston, then turning east to the 

 coast at Flamborough Head. The chalk is hard, similar in character 

 to a normal limestone, very porous, and strongly calcareous, except 

 where it is covered with boulder clay. Along the northern edge a bold 

 escarpment overlooks the Vale of Pickering, and another along the western 

 edge commands a view of the Vale of York, the strata dipping towards 

 the Plain of Holderness. On both slopes, dales are cut deeply into the 

 chalk. Many of these are dry and often covered with chalk and flint 

 gravel. The Wolds are highly cultivated, woodlands are few, and there 

 is very little natural vegetation. Areas of natural chalk grassland are 

 few ; the largest is Millington Pastures in the Londesborough district. 

 The escarpments and dales provide a suitable habitat for the beech, 

 which is a commonly planted tree, and Robinson, who refers to it as 

 ' the tree of the Wolds,' regards it as native. Owing to the extreme 

 porosity of the chalk, bogs and marshes are absent, and only around 

 the base do springs occur which afford habitats for aquatic and marsh 

 plants. 



East and south-east of the Wolds lies the Plain of Holderness, covered 

 entirely with glacial and alluvial deposits. A long tongue of land extends 

 to the south-east, ending in the hook of Spurn. Much of Holderness 

 is only a few feet above sea-level, its highest point being about 100 ft. 

 The soil is a stiff clay except for certain gravelly morainic ridges and 

 the alluvial valleys of the streams. The soil conditions favour agriculture 

 and market gardening and also afford good pasturage ; as a result practi- 

 cally the whole area has been changed by extensive drainage and culti- 

 vation, and little native vegetation persists. In strong contrast to the 

 previous divisions of the county heaths are absent. The species most 



