i66 CHEMICAL COMPOSITION OF THE SOIL [chap. 



the herbage is generally very varied and forms a thick 

 close sole. Buttercups are very common on some of 

 the alluvial pastures, and are sometimes taken as a 

 sign of overmuch cake feeding ; many Oxeye Daisies 

 {Chrysanthemum Leucanthemuni), on the contrary, indi- 

 cate that the land has been allowed to get too poor. 



Just as the sands pass insensibly into the loams, the 

 latter grade by degrees into the clays, the most pro- 

 nounced examples of which are the soils resting upon 

 some of the formation developed in the East Midlands 

 and in the east and south-east of England — the Oxford 

 and Kimmeridge Clays, the London and Weald Clays, 

 being the most marked. A true clay soil is cold and late, 

 very retentive of moisture yet suffering severely from 

 a drought of any duration, not only because of the cracks 

 it develops, but because of the slowness of the capillary 

 movement of water from below and the restricted root 

 development of all crops upon clay, especially when the 

 land has not been drained. Clays are difficult to work, 

 the draught of all tools being heavy, and great care 

 must be taken to catch them at the right moment of 

 working ; especially in spring it is ruinous to their tilth 

 to put horses on them when they are in the least wet. 

 It is most important to plough heavy soils in the autumn 

 and leave them rough through the winter, so as to get 

 the beneficial pulverising and flocculating action of 

 repeated frosts and thaws ; on the heaviest soils an 

 occasional bare summer fallow is desirable because of 

 the value of the weathering to the tilth. Being cool and 

 moist, clay soils are retentive of manure ; long straw and 

 other bulky manures are of value to open up the texture 

 of the soil ; it is often indeed of service to burn, or rather 

 char, some of the clay and incorporate it with the rest 

 of the soil. Clay soils are very often deficient in 

 carbonate of lime, so that dressings of lime are of 



