326 SOIL TYPES [chap. 



ammonia its full value as a source of nitrogen. The 

 lighter calcareous soils require a free use of nitrogenous 

 manures to get good crops. Calcareous soils are 

 generally well provided with phosphoric acid, owing to 

 the organic origin of the calcium carbonate ; the rule 

 is, however, by no means universal, the upper Chalk, 

 for example, yields soils with less than o-i per cent, 

 of this constituent. Superphosphate is undoubtedly 

 the best source of phosphoric acid for such soils, 

 basic slag is almost without action. The propor- 

 tion of potash present in these soils is generally 

 reflected in their texture ; if light and near the 

 unaltered rock, they are, as a rule, very deficient in this 

 constituent, and require its addition for the growth 

 of any of the root crops. Salt is generally bene- 

 ficial as an addition to manures on the calcareous 

 soils. 



The calcareous soils are generally warm, dry, and 

 healthy for stock ; when deep and sheltered they are 

 extremely fertile ; the thinner soils are rather subject 

 to certain insect pests, like the turnip flea. The abund- 

 ance of worms in chalky pasture is worthy of note. 

 The lighter calcareous soils are notoriously weedy. In 

 addition to the usual weeds of light land, Fumitory 

 {Fumaria officinalis), Geranium molle, and kindred 

 species, are almost confined to soils with a consider- 

 able proportion of calcium carbonate. Two crops 

 are very characteristic of calcareous soils wherever 

 the climate will admit of their growth, viz., sainfoin 

 and lucerne, which flourish excellently, and provide 

 abundant and valuable fodder even on the driest 

 chalk soils. 



The natural flora of these calcareous soils includes 

 the beech, yew, and wild cherry, among trees ; the 

 juniper, box, mealy guelder rose ( Viburnum lantana), 



