PLANT DISTRIBUTION AND ASSOCIATIONS. xliii. 



of grasses like Festuca ovina or Navdus stvicta, mingled with 

 Deschampsia flexuosa, Potentilla silvestris, Galium saxatile, and 

 similar turf-forming plants ; or heather may also be present in 

 varying amounts, though occupying a subordinate position, 

 and accompanied by bilberry and other peat plants ; or again, 

 on ill-drained level stretches like Erringden Moor the blue 

 moor- grass Molinia vavia may prevail, and along with it Erica 

 Tetralix, Juncus squarvosus, effusus, and conglomerate. Where 

 the grassy moor is contiguous to a heather moor, it naturally 

 approaches it also in the character of the vegetation ; so also 

 where it leads up to a cotton-grass moor, Eriophorum and 

 Empetvum naturally enter into the association. So much so 

 that the moor along Langfield Edge, where Festuca ovina is 

 dominant, is considered later as a variation of the cotton- 

 grass moor. 



The constant association of heather and bilberry and the 

 extreme latitude of their range, is one of the most marked 



features in the flora of the parish. They may 

 Heather be traced from the extreme east, between 



Moors. Brighouse and Elland at 200ft. or less, up to 



the top of Boulsworth Hill (1700ft.) beyond the 

 western border. No other plant is so widely distributed except 

 the grass Deschampsia flexuosa, which almost invariably 

 accompanies them. Yet their relative positions are always 

 changing under the combined influence of light, moisture, and 

 soil, and no association would better repay a careful examina- 

 tion of the conditions which are more favourable to one member 

 than the other. Their place in the oak woods has been already 

 discussed ; on the slopes of the cloughs above the woods it 

 seems impossible to say which is likely to be the more abun- 

 dant ; on the lower moor, however, the heather has a decided 

 advantage, which is lost again on the summits and highest 

 ridges. 



The heather moor then is one of moderate elevation, 

 and also of moderate humidity, and it may be added of 

 moderate extent. It is either a detached or isolated moorland, 

 or forms the outer ring bordering the wetter higher " mosses," 

 where cotton-grass alone prevails. Norland Moor and Ogden 

 Moor are the most familiar examples of it, but though parts of 

 Midgley, Heptonstall, Stansfield, and Rishworth moors are 

 heather-clad they are rather the out-lying spurs. Swill Hill 

 is a striking instance of an isolated heather moor, invaded in 

 parts by grass associations, but still retaining Tvientalis as one 



