A HISTORY OF BUCKINGHAMSHIRE 



vegetation belonging to the latter deposit and the pelophilous or clay- 

 loving species characteristic of the former. 



On Stoke Common we therefore find such plants as the all-seed 

 (Millegrana Radio/a), the dwarf willow (Salix repens), the alder buck- 

 thorn (Rhamnus Frangu/a), the meadow thistle (Cnicus pratensis), the 

 heaths Erica Tetralix and E. cinerea, the ling (Calluna Erica), the 

 petty whin (Genista angtica), the dwarf gorse (U/ex minor), the upright 

 pearl wort (Cerastium quaternellum-Mcenchid), the sedges Carex bhiervis, 

 C. echinata, the grasses Nardus sfricfa, Aira prcecox, A. caryopbyllea, 

 Deschampsia Jiexuosa, and Festuca ovina var. paludosa. 



On the elevated outlier at Lane End there is some marshy ground 

 where the marsh helleborine (Epipactis palustris), the bog pimpernel 

 (Anagallis tenella], the marsh lousewort (Pedicularis palustris), the sedges 

 Carex pulicaris, C. Jiava, C. ecbinata, C. Goodenoivii, and C. panicea, grow in 

 very near neighbourhood to the petty whin, the dwarf gorse, the ling 

 and the heath form of Orchis macu/afa, i.e. var. ericetorum, and where the 

 small winter-green (Pyrola minor) grows in short turf bordering a wood 

 in which the golden saxifrage (Cbrysosplenium oppositifolium) occurs. 



THE DRIFT. A casual glance at the geologic map, as coloured to 

 show the limitations of the various strata which come to the surface 

 in the county, does not reveal, as has already been stated, the true surface 

 soil over a great part of the area. In the north we find that both the 

 Oolite and the Oxford and other clays are sometimes covered with or 

 obscured by masses of clay full of pebbles, or by more or less extensive 

 patches of sands or gravels, and this is specially the case in the portion 

 drained by the Ouse ; indeed that river gives the name of the ' Ouse 

 gravels' to them. The influence of this covering upon the vegetation 

 has already been referred to. The brick-earth and clay with flints, 

 differing as it does materially from the bed rock in chemical composition 

 as well as in physical characteristics, also has great influence in changing 

 the character of the flora as we have previously seen. 



HIGH-LEVEL AND LOW-LEVEL ALLUVIUM. When rivers flow with a 

 gentle fall across flat country they are usually margined by tracts of flat 

 meadow-land, which are composed of materials carried down by the 

 stream and dropped whenever a slackening of the current prevents the 

 matter being carried further. Such deposits are known as Alluvium. 

 They may be gravelly, loamy or clayey. Their component parts are 

 purely local, being derived from the immediate neighbourhood of the 

 stream, so that in the meadows of Marlow or Windsor the alluvial 

 gravels contain a large percentage of the cretaceous rocks through 

 which the river has cut its way, and the only foreign elements are 

 such as are derived from the Drift or High Level Gravels which may 

 have been cut through and reassorted and mixed with those of purely 

 local origin. Hence we notice a remarkable difference between the 

 vegetation of the alluvial meadows of the Thames and of the Ouse ; 

 the latter being chiefly occupied by mesophytic plants, that is, such 

 as are almost ubiquitous or common to various situations, or by 



40 



