Page:VCH Berkshire 1.djvu/90

 A HISTORY OF BERKSHIRE of the main outcrop a small outlier is found at the base of Riever Hill, on which the village of Shalbourn is built. The richer and more fertile country afforded by this formation is plainly shown from the high chalk hills of Walbury Camp and the White Horse. The mouse-tail (Myosurus minimus), the hone-wort (Corum segetum) and the grass Bromus interruptus are found on it, and it gives the most northerly home in the county for the water dropwort (QLnanthe crocata). In the streams which issue from the base of the chalk escarpment a pond-weed (Potamogeton densuni) is a prominent feature. The presence of calcareous matter in the soil is shown by the occurrence of such eminently gypsophilous plants as the traveller's joy (Clematis), the candy-tuft (Iberis amara), the grass Bromus erectus, the striped toadflax (Linaria repens), and the thistle (Cnicus elio- phorus. On the Upper Greensand hops are cultivated in small quantity near Didcot, and there are very extensive orchards of plums, cherries and other fruit. THE CHALK, like the last two formations, extends right across the county from i o to 12 miles broad, and rises above the vale of Berks in a long graceful escarpment, forming by far the most striking physical feature in the county. This escarpment is indented by numerous narrow winding valleys, most of which are dry, and as viewed from the vale of the White Horse it presents the appearance of a long alternation of bays and promontories, which give it a striking resemblance to a coast-line, but there can be no doubt that its outlines are the product of subaerial denudation and not of marine action. The Dorchester or Wittenham Clumps are two outliers of the chalk on the upper greensand, and Windsor Castle is built on an inlying boss. In addition to the main mass of the Chalk there is a second area to the south of the Kennet, but this, although apparently distinct, is really conterminous with the Chalk of the central plateau, the beds of which, in their gentle southern slope, dip under the tertiaries of the Kennet valley to reappear at a more abrupt angle, and then form the line of picturesque hills of which Walbury Camp, 957 feet above the sea level, is the highest point. The chalk is also present in the south-east of the county from Sonning to Maidenhead, but the eminences in this area are capped with London clay. Where chalk actually comes to the surface we find rolling downs overgrown by short turf, which forms excellent pasturage. Over con- siderable extent of county this has been removed, and then the arable fields show great quantities of the yellow flowered mustard (Brassica alba), here called charlock, and four species of fumitory (Fumaria) have been found, Fumaria officinalis, F. parvijiora, F. Vaillantii and F. densiflora, as well as the candy tuft (Iberis amara), the sainfoin (Onobrychis), the chicory (Cichorium), etc. The turf offers in profusion the beautiful blue flowers of the milkwort (Polygala calcarea), the pink flowered squinancy wort (Asperula cynanchica], the blue Canterbury bell (Campanula glomerata], the purple flowered gentians (Gentiana germanica and G. Amarella), and here too the writer was fortunate enough to discover a new hybrid of these species which he has named G. Pamplinii. There are also the field rag- 44