XXXIV FLORA OF BERKSHIRE 



The Chalk. Chalk is a soft, white limestone, consisting largely of 

 the minute shells of Foraminifera, and more or less crumbled remains 

 of molluscs, echinoderms, and other organisms. The purer varieties 

 resemble very closely the foraminiferous ooze now forming on the bed 

 of the Atlantic ; they were deposited in a sea free from mechanically 

 carried sediment, but shallower than those in which the Globigerina 

 Ooze is now accumulating. 



The formation admits of the following subdivisions : — 



1. Upper Chalk with Flints. 5. Lower Chalk. 



2. Chalk Eock. 6. Totternhoe Stone. 



3. Middle Chalk. 7. Chalk Marl. 



4. Melloum Rock. 



From a general point of view we may say that the lower members 

 contain a considerable portion of clayey matter, but the proportion of 

 this decreases, and the rock becomes more and more a pure limestone 

 as we ascend in the series. The lower members of the Chalk form 

 a line of gently undulating hills rising sharply from the plateau of the 

 Upper Greensand. To the south of this the Upper Chalk stands up in 

 a bold escarpment, which rises to a height of 840 feet at the White 

 Horse Hill, and 959 feet at Walbury Camp \ known also as Coombe 

 Hill and Inkpen Beacon. This long line of escarpment is by far the 

 most striking physical feature in the county. It is indented by 

 numerous narrow winding valleys, most of which are dry ; and the 

 softly rounded outlines of the intervening hills are singularly graceful. 

 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 out- 

 lines are the product of subaerial denudation and not of marine 

 action. 



The Chalk, like the last two formations, extends right across the 

 county from west to east. On the west it is at least twelve miles in 

 breadth, that is from Hungerford to Compton Beauchamp. On the 

 east side of the county it reaches from Cholsey to Theale, a distance 

 of ten miles, but in this direction it is obscured by many patches of 

 more recent formations. In addition to this main mass of chalk there 

 is a second area, lying to the south of the Kennet. This area, although 

 apparently distinct, is really conterminous with the chalk of the 

 central plateau, the beds of which in their gentle southern slope (from 

 one to three degrees) dip under the Tertiaries of the Kennet Valley to 



^ The height of Walbury Camp is very differently estimated in topo- 

 grapliical works. Many authors ascribe to it a height of 1,011 feet, but the 

 lower height here given for it is taken from the more recent Ordnance 

 Survey. The county boundary of Berks and Hants crosses it at its highest 

 point. 



