A HISTORY OF DURHAM 



fall within the drainage tract of the Wear, and in the Auckland valley- 

 several very rich mines are worked. Thick seams of coal and the 

 fossilized remains of plants found in the carboniferous formation furnish 

 evidence of a luxuriant vegetation during this period. The fronds of 

 many species of ferns, fragments of the stems of Calamites, LcpidoJendron, 

 Picea, Pinites, Sigilaria, and Stigniaria are among the commonest forms 

 met with in abundance in a good state of preservation. 



As the moors diminish in extent they are replaced by pasture and 

 arable land. The general vegetation presents few features calling for 

 special remark. The rivers flow for the most part through deeply 

 excavated banks, and the many beautiful ravines and denes in which 

 shade plants love to shelter are characteristic of the whole county. The 

 country is richly wooded, and the numerous well-timbered parks, such as 

 Raby, Winyard, Ravensworth, and Gibside, boast some specially fine 

 trees. Large woods have been planted in some localities, chiefly of 

 Scotch pine and larch. A geological formation which has a marked 

 influence upon the character of the vegetation is the magnesian lime- 

 stone. Speaking generally, this occupies a triangular area eastwards of a 

 line from Shields to Piercebridge, and extending thence as far as the 

 coast, where it ends abruptly in a broken outline of outstanding cliffs. 

 The highest escarpment lies to the west. Between Sedgefield and 

 Darlington the general altitude attains some 300 feet, forming the 

 watershed of the Skerne, a river rising further northwards in the 

 magnesian limestone hills, near Trimdon, here reaching a height of 

 606 feet, their greatest elevation. The Skerne first flows eastwards, but 

 suddenly turns south-westwards at Hurworth, some six miles from the 

 sea, to follow a winding, sluggish course through Darlington, finally 

 joining the Tees at Croft. A large flat tract of country, consisting for 

 the most part of beds of red sandstone overlaid with boulder clay, 

 occupies this south-eastern part of Durham from Sedgefield to Hartle- 

 pool, and southward to the Tees. The ponds, ditches, and slowly 

 running streams of this district furnish very favourable stations for aquatic 

 plants. Morden, Bradbury, and Preston Carrs, through which the 

 Skerne flows, occupy the site of a former lake, now since the drainage 

 forming a large extent of peaty soil somewhat resembling the fens of 

 the eastern counties. Here, especially along the banks of the Skerne, 

 and around Billingham and Norton, the ditches abound in water plants, 

 among which may be specially mentioned the common meadow rue 

 [Thalictrum Jicivtim), the great spearwort {Ranunculus lltiguti), the water 

 crowfoot {R. Jluit(ins), the shining pond-weed {Potamogcton luccns), the 

 mare's-tail [Hippuris vulgaris), the water milfoil {Myriophyllum verticil- 

 latum), the glaucous stitch wort {Stellaria glauca), and the bur-marigold 

 {HiJcns tripurtita). The following are quite special to these localities, 

 and arc not known in the neighbouring county of Northumberland : the 

 frog-bit {llydrocharis Morsus-rana), the mud wort [Limosella aquatica), 

 the small creeping persicaria {Polygonum minus), the arrow-head {Sagittana 

 sagittifoUa), the great water dock {Rumcx hydrolupathum), the flowering 



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