Paleozoic Limestmie Soils 49 



Carboniferous or Mountain Limestone, developed in the 

 north of England, in North and South Wales, and in the 

 Mendip Hills of Somerset ; the vegetation of the English 

 areas of this has been carefully studied'. 



The Cambrian, Silurian and Devonian series all have 

 numerous limestone bands occurring at intervals between 

 other types of rocks; the vegetation of these however 

 has been scarcely investigated at all. The Magnesian 

 Limestone of Permian age occurs in Nottinghamshire, 

 Yorkshire, and other northern counties. 



The limestones generally form elevated land masses 

 or ridges, the valleys and slopes being usually occupied 

 by adjacent shales. On very steep slopes and crags, 

 where the products of chemical erosion by water contain- 

 ing CO2 are at once carried away, the rock is left bare 

 with characteristic plants occupying any spot where a 

 little soil can collect. On less steep slopes it is covered 

 by a very thin soil occupied by a special type of natural 

 grassland ("calcareous pasture")- Where the insoluble 

 products of chemical erosion are able to accumulate, as 

 on flat summits, on gentle slopes and in valleys, a deeper 

 soil results. On flat ground the Hme is often almost 

 completely washed out of this surface soil, with the result 

 that a heath vegetation occupies the area. Sometimes. 

 " limestone pavement " (p. 160) is formed on flat ground. 

 On slopes and in valleys scrub and woodland of character- 

 istic type occur. 



The rocks other than limestones (sandstones, grits, 

 mudstones, slates, shales, schists and various 

 "SUiceous crystalline rocks) are of extremely various 

 physical character and lithological compo- 

 sition, and the vegetation they bear is modified not only 

 by these factors, but also by the exposure and slope of 

 the ground, water supply, drainage and other factors. 

 In general, as already mentioned, they are characterised 



1 Smith and Bankin, 1903; Lewis, 1904; Moss, 1906. 

 T. 4 



