GEOGRAPHICAL DISTRIBUTION OF MOSSES. 79 



In the middle zone this region lies between 6,800 feet and 

 8,300 feet ; in the northern from 4,800 feet it descends 

 gradually to below 2,800 feet. Although the line of per- 

 petual snow does not touch our Scotch mountains, we have 

 snow-fields more or less extensive lasting through the 

 summer, as on Ben Nevis and the Cairngorm ranges ; and 

 we have some of the characteristic mosses, as Conostomum, 

 Bryum demissum, acuminatum, Ludwigii, Pottia latifolia, 

 Dicranum fulvellum, Grimmia contort a, elongata, and 

 montana, Andrecea nivalis, obovata^ Hypnum glaciale, H. 

 sarmentosum^ arcticum, etc. 



