A HISTORY OF DURHAM 



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

 disappear. Baker considers that the wild mignonette (Reseda lutea), 

 the wall rocket (Sinapis tenuifolia], the wild parsnip (Pastinaca sativa), 

 and three or four Cbenopodiacea, 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 (Ammopbila a rundinacea) , the rushy wheat- 

 grass (Triticum junceum), and 7". acutum, the sea lyme-grass (Elymus 

 arenarius), the sea-barley (Hordeum maritimum), the sea hard-grass 

 (Lepturus filiformis), the creeping fescue-grass (Festuca rubra), the 

 hemlock stork's-bill (Erodium cicutarium), and the three species of sea 

 sedges Carex arenaria, C. extensa, and C. distant. 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 (Pinguicula vu/garis) may be found growing equally well near 

 the Black Hall Rocks and at Langdon Beck. The wild thyme (Tbymus 

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

 also similarly distributed. The great water horsetail (Equisetum 

 maximum] and Gentiana Amarella 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 

 (Honkeneja peploides], the sea-holly (Eryngium maritimum), the hound's- 

 tongue (Cynoglossum officinale), and the red goose-foot (Cbenopodium 

 rubrum). 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 tripolium), the seaside 

 arrow-grass (Triglocbin 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 (Calluna vu/garis) 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 aquilina) everywhere adds 

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

 fern (Nephrodium Oreopteris) grows in great profusion, and sometimes 



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