IV. PHYSICAL GEOGEAPHY. 143 



perennial snow-patches or snow-drifts, without attaining 

 the true line of perpetual snow. The highest hills of 

 Perthshire rise almost to 4000 feet of vertical height ; 

 but no patches of snow are usually found on them so late 

 as July and August. The highest hills of Inverness and 

 Aberdeen exceed 4300 feet ; and on those hills, far below 

 the extreme summits, small patches of snow usually or 

 always remain unmelted until the new snow of another 

 winter again covers them. There is thus very little sur- 

 face which is constantly irrigated in summer by water 

 trickling over it at the temperature of melting snow. 

 Plants peculiarly adapted to such situations are conse- 

 quently almost absent from the flora of Britain. Saxi- 

 fraga rivularis and Stellaria cerastoides are perhaps the 

 nearest representatives of the plants alluded to. 



Some diversity of opinion, or rather inexactness of 

 knowledge, still exists in respect to the altitudes of the 

 highest hills. Recently it has been stated that the 

 highest summit, that of Ben Nevis, in Westerness, 

 slightly exceeds 4400 feet ; and that the summit of Ben- 

 na-muic-dhu, in South Aberdeen, falls short of 4300 feet. 

 More usually these two hills have been regarded as 

 nearly equal competitors for the first place in i)oint of 

 absolute height above the sea ; the priority between 

 the two being most frequently assigned to Ben Nevis. 

 Adopting the three latitudinal divisions before ex- 

 plained, their highest hills may be stated in English 

 feet thus : — 



S. Britain 3571. Mid Britain, 31G0. N. Britain 4374. 

 Supposing the two hills above mentioned to be respec- 

 tively the highest in the Western and Eastern divisions 

 of the island, then Ben Nevis may be said to give a slight 

 predominance of 100 feet, more or less, to West Britain. 

 There is probably a larger extent of surface elevated 



