54 The Soils of England and Wales 



ash- wood (see p. 167). Pasture, supporting large flocks 

 of sheep, covers large areas of the summits and many of 

 the slopes of the chalk downs. 



The arable land in which wheat is regularly included 



in the crop-rotation forming the "wheat- 

 oftne Chalk country" mentioned on pp. 28-29, is largely 



situated on the Chalk and the overlying thin 

 soils already described. The characteristic agricultural 

 method is based on what is called the "Norfolk four- 

 course system," in which wheat is followed by a "root- 

 crop" (turnips or swedes), this by barley, and the barley 

 by a "seed-crop," generally leguminous, such as alsike 

 (Trifolium hybridum) and white (T. repens) or red clover 

 (T. pratense), or a mixture of clover and rye-grass (Lolium 

 perenne). Oats are often substituted for wheat on the 

 lighter lands, and numerous other variations exist. This 

 rotation essentially depends on the "folding" of sheep 

 on the "green" crops and the manuring of the ground 

 by their droppings for the following cereal crop. This is 

 the characteristic feature of the agriculture of southern 

 and eastern England. The typical pasture of the South 

 Downs of Sussex, and of Salisbury Plain in Wiltshire, 

 supports great numbers of sheep, and in the down farming 

 the sheep feed sometimes on the pastures, sometimes in the 

 folds. The Chalk of the North Downs (Surrey and Kent), 

 and of Cambridgeshire, Norfolk, Yorkshire and Lincoln- 

 shire, has very much less (often practically no) open 

 " sheepwalk," the Chalk country in the four last-mentioned 

 counties being almost entirely arable. 



The outcrop of the Cretaceous rocks is not confined to 



the main belt running from south-west to 

 IntiJilt!'**'' north-east; there is an important extension 

 caused by a line of uplift running eastwards 

 from Wiltshire, through the counties of Hampshire and 

 Sussex, and across the English Channel to the neighbour- 

 hood of Boulogne in France. This line of elevation, known 



