county, and although this necessitates some repetition of plant names, yet the plan has the compensating advantage of showing how certain groups of plants are to be found on the same soils.
The geology of Buckinghamshire resembles very closely that of Oxfordshire, except that the Liassic formations are exposed to a much smaller extent in the former county, whereas the Reading beds and the London Clay are but sparingly represented in Oxfordshire, but cover considerable tracts of southern Buckinghamshire. The Lias Clay is shown in the north of the county between Grafton Regis and Castle- thorpe, owing to the Tove cutting its way down to it, but no very special vegetation marks the occurrence, beyond the growth of the ordinary pelophilous or clay-loving species. The Ouse, near Weston Underwood and Stoke Goldington, has also cut down to the Lias in two or three places, but again without exhibiting any plant of special interest. The Northampton Sands, which cap so many of the eminences of north Oxfordshire and west Northamptonshire, where from their porous nature they give a warm soil and afford a home for many heath-loving species, are practically unrepresented in our area, but the Great Oolite comes to the surface in many places, and in fact extends in a more or less broken band from Brackley and Buckingham in the west, by Potterspury to Newport Pagnell and Cold Brayfield in the east, and then passes into Bedfordshire. The contrast of the vegetation of that portion of country where the Great Oolite comes to the surface with that district where an impervious material, such as the Oxford Clay, forms the subsoil, is most marked. Nor is it the vegetation alone which marks the difference. In one case we find that the oolite has been quarried for building stone, so that we see good stone houses and cottages, often with thatched roofs since straw is more plentiful, which give a solid yet more picturesque character to the scene than the brick and slated houses of the clay district, while the stone walls of the villages, often mud-capped, afford a home for mosses and other plants to a much greater extent than the better pointed brickwork. The land too will be occupied more frequently by corn on the limestone and by pasture on the clays, and thus the latter is usually a thinly populated area, and such villages as do occur are often built upon some spot where a drift deposit gives some amount of porosity to the soil. If we pass through the county in the summer evenings, we may observe the white mist clinging to the clay surfaces, while the pastures on the limestones will be free. In comparing the more common plants we shall see on the Lime- stone that the hedgerows often contain the buckthorn (Rhamnus catharticus), the spindle tree (Euonymus europaeus), the wayfaring tree (Viburnum Lantana), and are often adorned with the traveller's joy (Clematis Vitalba), the maple (Acer campestre) and occasionally the glabrous fruited form, the cornel (Cornus europeaus), and here and there the bramble Rubus Radula, but the ubiquitous species is R. ulmifolius. Where clay is present the spindle tree and cornel will be rare and the traveller's joy absent, and the common brambles will be R. corylifolius and R. caesius, and there will be the bittersweet (Solanum Dulcamara) and the blackthorn
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