THE NATURAL HISTORY OF CHALK 



J. H. P. Sankey, b.sc. f.z.l. 

 Juniper Hall Field Centre 



Chalk, or calcium carbonate, is a kind of limestone. It is a massive rock with many 

 horizontal and vertical joints and fissures. It may be visualised as a sort of loosely jointed 

 solid sponge. Under it is a lining of clay (the Gault) which maintains a reservoir of water 

 within the Chalk which is readily permeable to rain falling on it. When the surface layers 

 and soil begin to dry the water can pass upwards by capillarity, and thus the whole rock 

 is permanently moist. Chemically the chalk is a base ; that is, it has the opposite pro- 

 perties to an acid which it will neutralise and it thus renders the soil "sweet" because the 

 loam is always base saturated. Chalk soil is typically shallow (except in some valleys) ; 

 it is rarely more than twelve inches in depth. The upper part is rich in humus and plenty 

 of base and there is usually a reasonable amount of moisture though water logging in 

 true chalk soils does not occur. 



The majority of plants favour a soil which is not deficient in base, hence the large 

 number of species of plants found on chalk soils — a contrast to many acid sandy soils. 



Chalk is a substance found throughout the animal kingdom. It is probably indis- 

 pensable to life, and it is of particular importance to some animals such as snails and others 

 requiring a high proportion of calcium carbonate in their bodies. 



The rich chalk flora together with the base saturated soil and humus supports a wealth 

 of animal life. 



One of the chief features of chalk vegetation is its ability to support a more or less 

 continuous flush of flowering plants from spring to autumn — a fact which bee-keepers 

 appreciate. Many of our rarer flowering plants, such as some of the orchids are strong 

 calcicoles, that is, they require a soil with plenty of calcium carbonate. And it is of interest 

 to note that the Chalk of Kent is favoured by many such rarities, for example, the lady 

 orchid, the late bee orchid and Polygala austriaca Crantz — a small species of milkwort 

 1,1a. Amongst the more familiar species common everywhere on Chalk must be mentioned 

 marjoram, salad burnet and yellow centaury ; there are many others. Traveller's joy 

 or Clematis is a good indicator of the presence of limestone and although beech is correctly 

 described as typical of chalk woodlands it occurs also on acid sandy soils. This gives 

 us th& concept of those plants which are exclusive to the Chalk 2 and those which are 

 characteristic, that is, they are found on other kinds of soil which are not derived from 

 limestone. Such plants are commonly those which require a soil which does not get too 

 wet ; beech, viper's bugloss and wood sage are examples. A third category of plants 

 can l3e recognised. This consists of those which are tolerant of a wide range of growing 

 conditions and which will grow on chalk soils as well as on wet and dry and acid soils. 

 Cleavers, self-heal, daisy and cock's foot grass are examples. 



The animals are also divisible into groups though most creatures have a much wider 

 range of habitats than plants. The obligatory calcicoles such as the Roman snail (which 

 curiously does not occur everywhere on Chalk) and round-mouthed snail are familiar 

 species. The rich snail fauna itself can be related to the presence of large quantities of 

 calcium carbonate and the abundance of the glow-worm is correlated with the large 

 numbers of small snails on which it feeds. Insects are much in evidence on the Chalk, 

 especially phytophagous beetles and many heteropterous plant bugs. Their presence is 

 associated with the rich herbaceous flora. The fact that certain food plants are exclusive 

 or characteristic of Chalk country restricts the range of some species. The chalkhill 



