156 Siib-formation of the Older Limestones 



The soil of limestone grassland is shallow, often being 

 only a few inches deep. In colour, it varies 

 from a whitish grey, where the lime-content 

 is very high, to a brownish or even reddish-brown where 

 the lime-content is lower and the iron-content high. 

 The more newly-formed soils have the higher lime- 

 content, and the older soils have the lower lime-content. 

 The newer soils are also dry and porous: the older 

 ones have often a comparatively high water-content. 

 Marshes occur here and there on the limestone hill-slopes, 

 so that the range of water-content on the calcareous 

 grassland is similar to that which occurs on the siliceous 

 grassland. However, in a general way, it is correct to 

 say that the soils of the calcareous grasslands are drier 

 than those of the siliceous grasslands. The water-content 

 of non-calcareous soils varies directly as the humus-content, 

 a result doubtless due to the water-absorbing properties 

 of humus. The water-content of calcareous soils, on the 

 other hand, is greater the less lime they contain. 



The two principal grasses (Nardus stricta and Des- 

 champsia flexuosa) of the drier type of 



erences siliceous grassland are quite absent from 

 from siliceous " t-.i ■ ■ ^ 



grassland. calcareous grassland, and so is the principal 



grass (Molinia cserulea) of the wetter type 



of siliceous grassland (cf. pp. 132-6). The bracken (Pteris 



aquilina), gorse {TJTex spp.), and the common rushes 



(Juncus effusus and ,/. conglomeratufi) which bring about 



such characteristic facies of the siliceous grassland, are 



only of local occurrence on calcareous grassland, and 



perhaps mainly confined in Derbyshire to leached soils 



or soils mixed with non-calcareous material. Many other 



plants characteristic of the siliceous grasslands are also 



alDsent from the calcareous grasslands, and the following 



list is a selection of the more widespread of these : 



Spergularia rubra Cytisus sooparius 



Polygala eerpyllaoea Genista anglica 



