64 



baker's north YORKSHIRE. 



whilst the dysgeogenous hills are more grassy and in the two 

 upper zones it is far more usually amongst the scars of the lime- 

 stone and the short grassy turf which the limestones immediately 

 underlie that the ascending stations of the common pascual, 

 pratal, mural and glareal plants of the low country are to be 

 found. A glance at the botanical list will show how very fre- 

 quently the ' Main Limestone ' and the ' Hambleton plateau ' 

 are mentioned in connection with the ascending limits of species. 

 And on the other hand, the heatherlands of the Central Valley 

 are all based upon sandstone, and with them Drosera anglica, 

 Vaccinium Oxycoccus, Listera cordata, Lycopodium Selago, L. 

 selaginoides and several of the Montane mosses descend to their 

 lowest stations, where they meet and mingle with such species 

 as Gentiana Pneumona?ithe^ Mentha Fulegiu?n, Centunculiis 

 7ninimus, Spergularia rubra, Cerasthun semidecandruni, Hyperi- 

 cum elodes, Radiola Millegrana, Ornithopus perpusillus, and 

 Lycopodium inundatiwi. 



It is in the tract of the Middle Oolite that the characteristically 

 Xerophilous species have their head-quarters. The following 

 species are the most typical representatives of this category and 

 are either absolutely or very nearly restricted in North Yorkshire 

 to the scars and dry banks" of the Middle Oolite, the Magnesian 

 Limestone, and the Mountain Limestone, avoiding altogether 

 or growing but very sparingly in the eugeogenous three-fourths 

 of the area of the Riding. 



LIST OF CHARACTERISTICALLY XEROPHILOUS SPECIES. 



Comparatively frequent species : 



Helleborus viridis 



Spiraea Filipendula 



Convallaria majalis 



Aquilegia vulgaris 



Pyrus Aria 



Carex digitata 



Actaea spicata 



Carduus eriophorus 



Sesleria caerulea 



Hutchinsia petreea 



Salvia verbenaca 



Avena pratensis 



Helianthemum vulgare 



Calamintha officinalis 



Bromus erectus 



Hypericum montanum 



Taxus baccata' 



Brachypodium 



Geranium sanguineum 



Orchis pyramidalis 



pinnatum 



Astragalus glycyphyllos 



Ophrys apifera 



Hordeum sylvaticum. 



,, Hypoglottis 



,, muscifera 





