24 Plant-life of the Oxford District 



characteristic ' calcicolous ' plants are found only in exposures of Coral 

 Rag. 1 



The Modern River- System. 



There is no reason to suppose that, during the known historical epoch of 

 1,000 years, there has been the slightest permanent change in the general 

 physical conditions of the climate or general topography of the district ; 2 

 and this fact has a suggestive bearing on the length of time included in 

 geological periods involving factors still in operation. Minor alterations 

 have been effected in the drainage system, and roads have made it more 

 accessible, but in biological essentials the district remains the same. The 

 alluvial plain is well irrigated by the branches of the Upper Thames (Isis) 

 and its tributary the Cherwell, both bringing water from outside the restricted 

 area considered ; the latter joining the Isis below the town at the Barges, 

 and by the artificial ' New Cut ', formed after the heavy flood of 1882, and 

 replacing an older channel a little farther down stream. Though carrying 

 down a considerable quantity of water in the course of the year, these rivers are 

 little more than shallow broad ditches, which in exceptional summers might 

 run wholly dry, 3 as undoubtedly they often did in the past. The summer 

 delivery of the Isis has been estimated at 73 million gallons per day, 4 and 

 the winter delivery as 320 millions. The City of Oxford requires about two 

 million gallons a day as water-supply, this being taken from the Isis above 

 the town near King's Weir. 



The Isis, flowing north at Stanton Harcourt from its junction with the 

 Windrush, breaks away to the east at Eynsham, picking up the Evenlode, 

 and rounds Wytham Hill to enter the old valley of the Cherwell, 2 miles 

 from the present stream at Oxey Mead, and turning sharply SSE. at King's 

 Weir it enters the Oxford valley from the NW. The main stream passes 

 Godstow and Port Meadow to Medley Weir and Osney Lock, through the 

 lower part of the city to Folly Bridge, Iffley, and Sandford. A loop of the 

 stream, breaking off at Hagley Pool, runs fairly parallel through Wytham, 

 Ferry Hinksey, and Botley. Collaterals and cross-connexions supply mill- 

 streams at Botley, Osney, and City Mills, and all these ramifications unite 

 below the town. With the junction of the Hinksey stream below Iffley, the 

 river is finally collected in a narrower channel before Sandford and Radley, 

 when it again turns west to Abingdon. This great lo-mile sweep of the 

 Thames, the broad areas of alluvial meadowland, and the meandering course 

 of the Cherwell with its own alluvium (NE.), constitute the more obvious 

 features of the river-system. The network of streams west of the city is 

 indicated by the fact that the road from the Castle to Botley, over a stretch 

 of alluvium a mile wide, formerly crossed 6-7 water-courses. The original 

 water-system has been increased by a canal to Birmingham (Oxford Canal 

 1769, completed 1790), running from the Castle Wharf north past Wolvercote, 



valley of the Bullingdon Brook (Cowley), and the Bayswater Brook and its connexions (Headington 

 Wick, Elsfield). Plot (1705), p. 65, clearly describes the cutting and drying of Peats, in one case 

 from a 4ft. seam. Sibthorp (1794), Flora Oxoniensis, describes Sphagnum as still growing 'in 

 Peat Bogs on Bullington Green '. Special interest also attaches to a seam of Lignite (4 in.) at 

 Kidlington, described by Plot (p. 66, loc. cit.), as indicating how the plant-remains of the soil-surface 

 have been already hunted through and exploited. The organic content of such alluvial soils may be 

 considerable, and requires to be examined for different areas and depths: e.g., samples dried at 

 100 C. gave Bullingdon Bog Valley, mole-casting, 21-52 per cent. Iffley Lock Field, mole- 

 casting, 21.12 per cent, (taken near the ditch, an old water-course). Cherwell alluvium, surface-soil 

 of hay-field, 77 per cent. (W. R. Day). 



1 Carduus nutans, Cirsium eriopkorum, C. acaule, Helianthemnm vulgare. 



2 The frost of Dec. 1142 was probably no more severe than that of March 1895, and the con- 

 dition of the water-meadows, particularly above Wolvercote, is much the same as at the time of the 

 Domesday Book. 



s In August 1893 the bed of the river was dry at Folly Bridge, and the steamers ceased to run ; 

 in 1921 the Cherwell was dry in places, stagnant for miles, with green mantle of Lemna. 

 4 Prestwich (1876), Water-supply of Oxford, p. 39. 



