YORKSHIRE PLANT ECOLOGY 25 



the dominant tree is ash, but beech is abundant and grows well and to 

 a large size. If beech is native in the county (and that is doubtful) the 

 Permian tract, also the slopes of the Chalk Wolds, provide good con- 

 ditions for its development. Natural woodlands do not occur, but 

 there are extensive parklands and plantations with fine trees in great 

 variety, and Studley Park, near Ripon, contains most of the woodland 

 trees grown in Britain. 



The few uncultivated lands are either hazel copse or grassy common, 

 as Hook Moor, near Aberford. Typical examples of Permian vegetation 

 may be seen at Thorpe Arch, Boston Spa, Jackdaw Crag and the neighbour- 

 hood of Knaresborough ; the more interesting shrubs in the hedgerows 

 are barberry, holly, maple, spindle tree, purging buckthorn, and black- 

 thorn, and of herbaceous species found on this tract are Anemone Pulsa- 

 tilla, Helleborus viridis, Actcea sptcata, Reseda lutea, Helianthemum vulgare, 

 Cerastiutn aquaticum, Arenaria tenuifolia, Linum perenne, Geranium 

 sanguineum, Sison Amomum, Pastinaca sativa, Asperula cynanchica, 

 Dipsacus pilosus, Arctium intermedium, Inula Conyza, Carduus eriophorus, 



C. acaulis. Campanula patula, Chlora perfoliata, Atropa Belladonna, 

 Linaria Elatine, Calamintha Nepeta, Hottonia palustris. Daphne Laureola, 



D. Mezereum, Orchis pyramidalis, Ophrys apifera, Spiranthes autumnalis, 

 Carex divulsa, C. digitata, C. ornithopoda, C. strigosa, and Brachypodium 

 pinnatum. 



Most of the above species are of special interest when we consider 

 their distribution in Britain, and when indicated on a map the Permian 

 ridge is seen to be a great line of postglacial migration or persistence 

 of southern species which reach their northern limit in Yorkshire. Exclud- 

 ing critical genera and species, about sixty-five species reach their northern 

 limit in Yorkshire and twenty more species reach their limit across the 

 Tees in Durham, and their distribution can be traced along the ridge, 

 then eastwards to the calcareous Hambleton and Howardian Hills and 

 chalk Wolds, and westwards to the mountain limestones of Upper Wharfe- 

 dale and Upper Teesdale. Along the great tract of Grits and Coal 

 Measures these species are almost absent. On the other hand northern 

 species reaching their southern limit in Yorkshire find their chief centres 

 on the limestones of Upper Teesdale and the north-western dales, to a 

 less extent on the calcareous eastern dales and to only a slight extent on 

 the Permian, Millstone Grits and Coal Measures. 



The north-eastern or Oolitic hills include the Hambleton and Howardian 

 Hills bordering the Vale of York and the North York Moors and Cleve- 

 land Hills. The glacial geology of this area has been admirably described 

 by P. F. Kendall and the natural history and vegetation by F. Elgee. 



The North York Moors rise to over 1,400 ft. and the subsoil is formed 

 from the sandstones and shales of the Lower Oolite. Running in a 

 synclinal depression of the Oolite is the Esk. Its principal tributaries 

 join it from the south and form a succession of dales cut down into the 

 Lias ; the main ones are Basedale, Westerdale, Fryupdale, and Glaisdale, 

 and near the coast, Iburndale. The Cleveland Moors are the finest 

 heather moors in Yorkshire ; ling is the dominant plant, but in the 

 moister hollows and slacks bell-heather and cottongrass predominate, 



