Chalk and Clay-with-flints 53 



The Lower Greensand, whose outcrop is a narrow 

 interrupted belt at the base of the series, forms in places 

 a distinct sandstone escarpment. This rock varies much 

 in lithological character, and its vegetation is complicated. 

 It is followed by the Gault, a heavy clay, sometimes cal- 

 careous, which may bear the damp type of oakwood, and 

 is now largely pasture-land. 



The Chalk, the most important member of the Cre- 

 The Chalk taceous series, is on the whole a very pure 



soft limestone forming more or less elevated 

 masses of characteristic gentle rolling contours (downs) 

 and fairly steep escarpments. The Chalk occupies a large 

 area in southern and eastern England. In no case does 

 the Chalk attain a height of 1000 feet (305 m.), though 

 it often exceeds 500 feet. 



The Chalk plateaux of the south are often overlaid by 

 large areas of a deposit known as " clay-with-flints," which 

 is of variable composition, usually a loam, sometimes a 

 heavy clay and sometimes sandy, and typically contains 

 numerous flints. It is supposed to represent the insoluble 

 residue of the dissolution of a great depth of overlying 

 chalk, though in some cases it may be the remains of 

 Tertiary formations which once lay on the top of the 

 Chalk. The Clay-with-flints is generally very deficient 

 in lime. It is largely arable land, which is much im- 

 proved by liming or treatment with the artificial manure 

 known as basic slag'. The natural vegetation is oak- 

 wood of various types corresponding to the various soils. 

 Heath is sometimes developed on the lighter poorer soils. 



Where the chalk itself forms the immediate subsoil, 

 the soil itself is extremely thin, often only 2 to 5 inches 

 (c. 5 to 12 cm.) in thickness, and is frequently ex- 

 tremely poor in lime. In the south-east the natural 

 vegetation is beechwood on the slopes of the escarpments 

 and valleys; towards the south-west this passes into 

 ' Mainly phosphate of lime. 



