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 A HISTORY OF SURREY The ten districts into which the county is divided are : (i) Black- water; (2) Bourne Brook; (3) Upper Wey ; (4) Lower Wey ; (5) Upper Mole; (6) Lower Mole; (7) Hogg's Mill; (8) Wandle ; (9) Medway all of which drain into the river Thames ; and (10) Arun, draining into the English Channel. These are now described, and lists of their rare or characteristic species are appended. 1 . BLACKWATER This district is bounded on the south by a line leaving the Hants border at Lower Old Park, and extending to a point on the Hog's Back a little north-east of Scale ; thence the eastern boundary runs past Ash Green station, the Fox Hills and Chobham Ridges to the bor- ders of Berkshire. The other boundaries are formed by the counties of Hants and Berks. This is a small district, comprising as it does only a limited portion of the river basin. For the most part it consists of more or less barren and uncultivated sandy heaths, interspersed with considerable tracts of deep and dangerous peat bog. On the former the three heaths (Calluna vulgaris, Erica cinerea, and E. tetralix), with the furze (Ulex eurepaus and U. nanus) and the broom (Cytisus scoparius), form the bulk of the vegetation, together with extensive pine woods which cover much of the higher ground. A boggy wood adjoining the railway and canal near Ash Vale is remarkable for the various species of sedges which grow together there and which are not usually associated, such as Carex elongata and C. riparia ; the latter however appears rarely to flower, so that its identity was not certainly made out for several years. In the alluvial meadows by the river Blackwater between Frimley and Blackwater there occurs a small quantity of the great burnet (Sanguhorba officinalis), not known elsewhere in Surrey ; while in a deep bog near the canal at North Camp the slender cotton-grass (Eriophorum gracile) grows in abundance, its discovery here restoring the species to the county list. The generally boggy nature of the land is indicated by the occurrence of such plants as the meadow thistle in several places on the railway banks, while the alder (Alnus glutinosa) quite replaces the more familiar hawthorn in long sections of the railway hedges. As an absentee from the greater portion of the district the common primrose (Primula vulgaris) may be mentioned ; this plant, so widely distributed over the county and often so abundant, is quite unable to exist on the hot dry sand of the Bagshot series, and is only found in the neighbourhood of the chalk with the exception of one locality near North Camp, where it occurs on alluvial soil by a small stream. The following are among the more remarkable and interesting plants found in this district : Ranunculus tripartitus, DC. Potamogeton nitens, Weber. var. intermedius, Hiern. ruiescens, Schrad. Cerastium tetrandrum, Curtis trichoides, Cham. Sanguisorba officinalis, L. Scirpus pauciflorus, Lightf. Anthriscus vulgaris, Pers. Eriophorum gracile, Koch Pyrola minor, L. Carex elongata, L. Wahlenbergia hederacea, Reich. canescens, L. Utricularia neglecta, Lehm. fulva, Good. minor, L. Oederi, Auct. Myrica Gale, L. Agrostis setacea, Curtis Potamogeton heterophyllus, Schreb. 2. BOURNE BROOK The Bourne Brook district is bounded on the west by district i, on the north and north- east by the county of Berks and the river Thames, and southwards by a line starting from Chobham Ridges and passing near Bisley and through Horsell to a point on the river Thames about midway between the mouths of the Bourne Brook and river Wey. The stream from which the district takes its name rises close to the village of Bagshot, uniting a little north of Horsell with another branch which rises on Bisley Common, and flowing in a north-easterly direction to its junction with the river Thames. The general character both of the soil and vegetation is very similar to that of district I, except that the bogs are more extensive. One feature may be noted which is quite unique in the county. As one crosses the wide expanse 40