A HISTORY OF DURHAM 



a second time, and so when fresh importations cease they rapidly 

 disappear. Baker considers that the wild mignonette {Reseda luted) ^ 

 the wall rocket (Shiapis tenuifolid), the wild parsnip {Pastinaca sativd), 

 and three or four Cheriopodiacca, are all that are likely to have been 

 introduced in this manner. The sand dunes are covered with the grass- 

 like associations of sand-binding plants specially adapted for this situation 

 by their deep roots and creeping rhizomes. Chief amongst these may 

 be mentioned the sea-reed [Amtnophila arutidinaced), the rushy wheat- 

 grass [Triticum junceum), and T. acutum, the sea lyme-grass [Elymus 

 arenarius), the sea-barley [Hordeum niaritimum), the sea hard-grass 

 [Lepturtis Jiliformis), the creeping fescue-grass {Festtica rubra), the 

 hemlock stork's-bill {Krodhim cicutarium), and the three species of sea 

 sedges — Carex arenaria, C. extensa, and C. distam. A more varied flora is 

 found upon the steep grassy slopes with a wet argillaceous subsoil. 

 Here many plants which are well represented in the vegetation of the 

 upper dales are found in abundance. The graceful ' grass of Parnassus ' 

 [Parnassia palustris) and the glossy yellowish-green rosettes of the 

 butterwort [P'wguicula vulgaris) may be found growing equally well near 

 the Black Hall Rocks and at Langdon Beck. The wild thyme [Thymus 

 Serpyllum), the seaside plantain (Plantago maritima), and many others, are 

 also similarly distributed. The great water horsetail [Eguisetum 

 maximum) and Gentiana Atnarella are again characteristic plants found 

 plentifully here and at a considerable distance inland. Just above the 

 tidal limits some of the most characteristic maritime plants found are : the 

 sea-rocket [Cakile maritima), the beet [Beta maritima), the sea-purslane 

 [HoTikeneja peploides), the sea-holly [Eryngium maritimum), the hound's- 

 tongue [Cynoglossum officinale), and the red goose-foot [Ghcnopodium 

 rubrutn). The yellow horned poppy [Glaucium luteum) was once plentiful 

 near Seaton Carew, but it is feared that it is now extinct. Peculiar 

 to the salt marshes are the sea-starwort [Aster tripoliuni), the seaside 

 arrow-grass [Triglochin maritimum), the sea-blite [Suceda maritima), and 

 the shrubby sea-purslane [Obione portulacoides). On the limestone cliffs, 

 the sea spleenwort [Asplenium marinum) must be specially mentioned, 

 but it now grows only in the more inaccessible situations. 



The district coming within the drainage tract of the Derwent 

 extends to the north of the county. The hills are chiefly composed of 

 millstone grit overlying the carboniferous limestone strata, and in the 

 upper part have much the same undulating heathery character as the 

 fells already considered on the west. The sandstone, however, appears 

 more dominant, and the moors consequently are more thickly clothed 

 with heather, the ling [Calluria vulgaris) and Erica cinerea being the 

 most abundant species. The brilliant purple of the heather on these 

 vast sweeps of moorland, and in the spring the perfect blaze of yellow 

 broom, produce an impression of vivid glowing colour which is not 

 readily effaced. The common bracken [Pteris aquilimi) everywhere adds 

 its wealth of orange-coloured fronds in autumn. The mountain liuckler 

 fern [Ncphrodium Oreoptcris) grows in great profusion, and sometimes 



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