38 INTRODUCTORY EXPLANATIONS. 



upon single characteristics. Keeping tliis in view, the 

 thi-ee zones may be shortly explained here, and the more 

 complete descriptions.be aftenvai'ds given. 



The Super-agrarian zone may be said to comprise thi'ee 

 portions of the sm-face of Britain. Fn-st, all the coast-line 

 and low plains or moors in the north and north-west of 

 Scotland, where we find plants of an alpine chai-acter de- 

 scending even to the sea-shore ; such as Thalictnun alpi- 

 num, Draba incana, Saxifraga oppositifolia, iVibutus alpina 

 and Diyas octopetala. Secondly, all other spaces, in any 

 part of Britain, where the elevation of the gi'ound leads to 

 the production of the same or usually associated species ; 

 Arbutus Uva-Ursi, Saxifi-aga stellaris, AlchemiUa alpina, 

 Tofieldia palustris and Jimcus triglumis being examples of 

 the latter. Tliudly, those tracts of slight elevation, upon 

 which a coiTesponding flora and general vegetation prevail, 

 apparently in consequence of mere proximity to high moun- 

 tains; Saxifraga aizoides growing so low as 300 feet among 

 the mountains of Cumberland, and EpUobium alsinifoUum 

 at 500 or 600 feet in Caemarvonshii'e ; although these 

 plants are never seen at such a low elevation in England, 

 remote from the higher hills. In addition to these species, 

 derived from the arctic region, tliis upper zone of the 

 agraiian region is chaiacterised (in descending) by the 

 appearance of Bex, Corylus, Quercus, Fraxinus, Lonicera, 

 Crataegus and fiTiticose Rubi ; equally so, likewise, by 

 the absence of other species wliich are not seen until we 

 descend into the next lower zone. 



The Mid-agrarian zone wUl comprehend all the low 

 gi'oimds, clear from the momitains, which are situate 

 between the estuaries of the Clyde and Tay, on the north, 

 and those of the Humber and Dee, on the south ; also, 

 probably, a narrow coast-hne of the East Highlands, ex- 

 tending from Perth to Aberdeen, and, possibly, even to 



