A HISTORY OF BERKSHIRE northern portion is composed of grassy downs with softly curving out- lines, or of the more undulating tracts which have been brought under cultivation. Further south the chalk becomes covered with ' clay with flints ' and ' brick-earth,' and is often a woodland tract, and extensive heathlands prevail where the tertiaries are present, and boggy ground where these are impervious. From the base of the porous chalk copious streams of water issue, in which large quantities of water cress are grown. READING BEDS. The lowest tertiary strata found in Berkshire consist very largely of stiff clay, but also include beds of sharp sand and loams. These beds once formed an unbroken sheet extending over the whole of the chalk, but they have been largely swept away by denudation, and beyond their main mass a very large number of outliers testify that they had formerly a much wider range. They are now found scattered over a large area of southern Berk- shire, and are shown on the geological map. The varied soils formed by them necessarily give rise to a varied vegetation, which includes several local species, but as the beds are much broken up it would not be easy, even if desirable, to keep their flora apart from that of the other members of the tertiary beds. The extensive deposit of drift gravels with which they are often covered also increases the difficulty of keeping the flora of the ' Reading Beds ' distinct. One must content oneself by saying that where the * plastic clay ' is the pre- dominating surface, there plants which prefer an argillaceous soil will be found, so that the bladder sedge (Carex vesicaria) and the greater spear-wort (Ranunculus Lingua) appear in ponds on the clay of the ' bottom bed ' near Marlstone and Yattendon ; in Oare Woods the pale sedge (Carex pallescens) is to be found. South of Newbury, in ponds, the pennyroyal (Mentha Pulegiuni) occurs ; at the base of the Wargrave outlier is a marshy spot which gives a home for the tussock sedge (Carex pantcu/a fa), etc. On the sandy portions of the beds sand- loving arenaceous plants are necessarily found, such as the cudweed (Filago apiculata), the clovers Trifolium striatum and T. arvense, the bird's-foot (Ornitbopus perpusillus), the hawkweeds Hieracium boreale^ H. sciaphilum and H. umbellatum. The drift gravels which overlay these Reading Beds give a specially interesting flora, as from the absence of rich pasturage and the more exposed condition of the surface soils such local species as the cinquefoil (Potentilla argentea), the clovers T. scabrum, T. subterraneum, the pinks Dianthus Armeria and D. deltoides, the centaury (Erythrcea ramosis sima] , and the scabious (Jasione montana) are found, as well as a very varied bramble flora. THE LONDON CLAY is a thick mass of a bluish or greyish clay, which weathers brown on the surface, and has a broad outcrop in Berk- shire. The range of hills from Cold Ash Common to Mare's Ridges consists very greatly of this formation. There are several outliers north of the Kennet, such as the large area of Bucklebury Common, where the clay is much obscured by drift gravels. South of the Kennet the 46
