Calamus) is probably native, and the narrow-leaved reed-mace (Typha angustifolia) occurs. The sedges include Carex acuta and C. paniculata, and Sparganium mglectum as well as S. erectum occurs; and the beautiful meadow crane's-bill (Geranium pratense) is not uncommon, while the willows include Salix caprea, cinerea, triandra, alba, viridis, fragilis, aurita, Smitbiana and purpurea. Near Moulsoe the graceful Carex Pseudocyperus grows, and the water-stitchwort (Stellaria aquatica) is rather common. The horned pondweed (Zannichellia palustris) is not unfrequent and the wet pastures are often full of Juncus glaucus. Characteristic plants in addition to those alluded to which grow upon this formation are the ox-tongue (Picris echioides), the marsh stitchwort (Stellaria palustris), the honewort (Sison Amomum), especially where a little gravel is also present, the yellow cress (Roripa palustris), the hemlock (Conium maculatum), and the black poplar (Populus nigra), which is extensively planted, probably in some cases from the fact that in the early days of our railway system buffers for goods-wagons made of this wood were found to bear the concussion better than almost any other timber.
The Coralline Oolite forms in Oxfordshire and Berkshire a conspicuous ridge stretching from west to east, on which many rare and interesting species grow, but when it reaches Buckinghamshire it thins out and changes its character so greatly as to be scarcely recognizable, and is chiefly represented by a clayey band which may be followed by Worminghall, Oakley, round Muswell Hill, and through Dorton to the base of Quainton Hill, and it may exist in a transitional state at Studley. Instead of the sandy or calcareous soil of a very changeable nature which characterizes the surface soil on the formation in Oxfordshire, there is a more uniform and a much poorer soil on the fragmentary beds of the Coralline Oolite in Buckinghamshire, so that we miss such species as the round-leaved crane's-bill (Geranium rotundifolium), the hybrid poppy (Papaver hybridum), the climbing bindweed (Polygonum dumetorum) and many other species which are found in Berkshire or Oxfordshire.
The Kimeridge Clay. In Oxfordshire and Berkshire this formation is quite distinct from the Oxford Clay, since the Coralline Oolite just alluded to keeps them apart, so that we have in those counties plants which are fond of warmer and a more pervious soil abundantly growing on the old coral-reef which rises above the two clay deposits; but as we have seen in Buckinghamshire, the Coralline Oolite has either entirely thinned out or has been so modified in character as itself to form a clay band. There is nothing over the greater part of north Bucks to divide the great extensive clay deposits from each other, and in some parts, as near Stewkley, the separation of one from the other is described on the Geological Survey as wholly conjectural.
So far as the formation influences plant distribution we may say that what is true of the Oxford is also true of the Kimeridge Clay. The surface is likewise uninteresting and undiversified; few rare plants occur; the absence of springs means that there are no bogs, and such marshes as occur are too sour or rather have the waters too charged with
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