BOTANY 



GENERAL PHYSICAL CHARACTER OF THE COUNTY WITH 

 RELATION TO THE FLORA 



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^HE physical features of Durham, which embrace a wide range of 

 altitude, exercise an important influence upon climatic conditions, 

 and together with the different geological strata tend to produce 

 an extremely rich and varied flora. A glance at the Orographical 

 Map will show the general configuration and boundaries of the county. 

 The zones of altitude extend through three of the six zones into 

 which H. C. Watson, in his work on Botanical Geography, divides the 

 surface of the county ; these corresponding to his mid-agrarian, super- 

 agrarian, and infer-arctic zones. Following Baker's scheme these may be 

 described as the Lower, Middle, and Upper Zones, the Lower including 

 the heights up to 900 feet, the Middle those between 900 feet and 

 1, 800 feet, and the Upper the heights beyond that level. 



At the western extremity of the county, where its width contracts 

 to only I o miles, the two great river systems take their rise, this neck of 

 land embracing the whole of the Wear watershed, and half of the tract 

 drained by the Tees. The latter has its actual source in Cumberland, 

 rising east of Cross Fell (2,900 feet) some few miles west of the district, 

 and enters the county at a high moorland region 1,600 feet above sea- 

 level. This is a wild, desolate expanse, which northwards, beyond the 

 Crookburn, extends into a series of lofty ridges of similar character, 

 presenting the most mountainous aspect of the whole county. These 

 high grassy and heathery peaks sweep boldly round the head of the dales, 

 the most elevated points from south to north including Viewing Hill 

 (2,097 feet), Highfield (2,322 feet), Burnhope Seat (2,546 feet), Dead- 

 stones (2,326 feet), Knoutberry Hill (2,195 feet), Nag's Head (2, 207 feet), 

 and Kilhope Law (2,206 feet), which last commands the extreme north- 

 west of the county. From this eminence a fine view is obtained over the 

 Cheviots and Allenheads in the Northumberland border. On the southern 

 flank of Burnhope Seat is found the weird-looking tract of Yad Moss, a 

 wild expanse of peat, covered with a very scanty vegetation and broken 

 up by deep rifts cut in the black peat to its foundation of shaley sandstone, 

 indicating in a remarkable manner the great force of the western gales. 

 A succession of peaks of gradually declining altitude form undulating 

 ranges of hills proceeding eastwards, one of which, north of the Wear, 

 forms the watershed between that river and the country drained by the 



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