2 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



grains of quartz, and hence the soils derived from them tend to 

 be light, and are often not sufficiently retentive. Many sand- 

 stones, however, contain larger or smaller proportions of 

 argillaceous matter diffused through them, and may then yield 

 loamy soils of good quality. Now and again we meet with 

 sandstones which have been derived more or less immediately 

 from the breaking-up of such rocks as granite, gneiss, etc. Such 

 sandstones often contain much decomposing felspar, and various 

 more or less altered ferro-magnesian minerals, particularly mica — 

 from which soluble alkalies and alkaline earths are obtained. 

 Few sandstones, indeed, do not contain scales of mica, which are 

 often so plentiful as to give the rock quite a fissile structure. How- 

 ever abundant such minerals may be in a sandstone, they are not 

 often conspicuous in the overlying subsoil, while they are wholly 

 wanting in the vegetable soil. It is obvious, in short, that they 

 become decomposed, and in the process yield compounds available 

 for plant-food. Many sandstones owe their induration to some 

 cementing material which binds the grains together. This 

 material may be calcareous, ferruginous, or argillaceous. When 

 such rocks are weathered, therefore, the nature of the cementing 

 material necessarily affects the character of the soil. There are 

 certain very old arenaceous rocks, which contain so large a 

 proportion of argillaceous material that the soils formed upon 

 them are often rather clays than loams. The rocks referred to 

 are termed greyivackc by geologists. They are relatively hard, 

 greyish-blue or greenish as a rule, and are known to the country 

 folk as wJmistones. The Lammermuirs, the Lowthers, and other 

 hill-ranges in the south of Scotland are built up very largely of 

 these rocks. Although the soils derived from greywackes are not 

 infrequently too retentive, yet here and there, when they can be 

 well drained, they are cultivated with success. It may be added 

 that greywackes not infrequently contain considerable porportions 

 of felspathic material, the decomposition of which naturally 

 enriches the soil. 



Sandstones may occur either in thick massive beds or in 

 thinner strata, and the individual beds are very frequently 

 separated by intervening layers of argillaceous shale. Hence 

 when a series of sandstones and shales crop out at the surface, 

 the soils derived from both sets of beds eventually become 

 commingled. This, of course, is due to that movement of soil- 

 materials which is always in progress. Thus in regions where 



