soil: its origin and nature. 19 



as conditions of climate and surface-slope are favourable or the 

 reverse, the soil may be good or practically barren. In this 

 country the rock is largely confined to the Highlands, and 

 therefore it is only here and there that its disintegrated and 

 ■decomposing materials are allowed to remain for any time 

 in sihi. 



Mica-schist. — This rock is also largely restricted to our 

 mountain districts. Typical mica-schist, consisting of quartz 

 and mica only, weathers slowly, and the thin soils derived from 

 it are generally of poor quality. But not infrequently many 

 accessory ingredients are more or less plentifully present in 

 mica-schist — such as felspar, garnet, apatite, and sometimes 

 calcite. When the gradients are favourable, the soils derived 

 from such mica-schists may be as good as or even better than 

 those yielded by granite and gneiss. They are often rather 

 loams than clays, and under favourable conditions have proved 

 to be fairly fertile. 



Now and again we encounter schistose rocks which have 

 essentially the same composition as some of our dark-coloured 

 basic igneous rocks, and the resulting soils in such cases are 

 dark loams of good quality. Unfortunately, the rocks referred 

 to {amphibolites) are somewhat sparingly developed in Scotland, 

 occupy no large areas, and often occur at relatively high 

 elevations — being confined to our Highland areas. 



The only other metamorphic rocks that need be referred to are 

 clay-slate and quartzite — both of which occupy considerable areas 

 in the Highlands. The former consists essentially of silicate of 

 alumina, and its disintegrated materials, therefore, usually form a 

 cold, wet, sterile clay. Occasionally, however, owing to the 

 presence of felspathic and micaceous ingredients, the soil is of 

 a less forbidding quality. As quartzite consists essentially of 

 ■quartz, its disintegrated debris forms at the best only a thin, 

 meagre, sandy soil. 



3. Derivative Rocks. — In this division many varieties of rock 

 are placed. Some, however, are but sparingly developed, and 

 need not be here considered. Excluding these, we may say that 

 the great majority consist either of arenaceous, argillaceous, or 

 calcareous materials. 



Arenaceous Rocks. — The most characteristic of these rocks are 

 the sandstones, of which there are many varieties. The great 

 majority are quartzose, that is to say, they are made up chiefly of 



