40 INTRODUCTORY EXPLANATIONS. 



to be received as characteristic. Examples occur in Erica 

 ciliaris, Sibthorpia europaea, Cyperus longus and Scilla 

 autumnalis. 



The six cUmatic zones, into which the two regions are 

 thus sub-divided, may be better understood and remem- 

 bered after being presented to the eye in connexion with 

 each other. The Nos. are reversed, because it is more 

 convenient to trace them upwards, fi-om south to north, 

 from low to high ground : — 



II. Arctic Region. 



(!. Super-arctic zone — Salix herbacea, without Calluna. 

 f>. Mid-arctic zone— Calluna vulgaris, without Erica. 

 4. Infer-arctic zone — Erica Tetmlix, without Pteris. 



I. Agrarian Region. 



3. Super-agrarian zone — Pteris aquilina, without Rhamnus, &c. 

 2. Mid-agrarian zone — Rhamnus catharticus, without Clematis. 

 I . Tnfer-agrarian zone — Clematis, Rubia, Cyperus longus. 



Unless the highest part of Snowdon can be deemed to 

 attain the super-arctic zone, none of the before-explained 

 provinces will include the fliU series of six zones. Else- 

 where the hills are not sufficiently lofty to pass the mid- 

 arctic zone, imtil we arrive at the Highland provinces, all 

 three of which have their highest summits clearly above the 

 limits of the Calluna; but the lowest portions of these 

 provinces, near their coast-line and southern boundary, fall 

 barely within the mid-agrarian zone. The six various 

 shadings in the annexed diagram (repeated from page 14) 

 wUl indicate the succession of zones ; their true limits, re- 

 latively to altitude, being yet unascertained in most of the 

 provinces. The little map is on too small a scale for the 



