
382 STRUCTURAL AND FIELD GEOLOGY 
for existence on the meagre gritty clay- soils derived from 
the granites and gneisses of the same region. 
Amphibolites—These rocks are essentially aggregates of 
amphibole (hornblende, actinolite), but many other minerals 
are often present. They yield dark loamy soils of excellent 
quality, quite similar in character to those of the diorites and 
basalts. The rocks, however, do not occupy large areas in 
Britain, and are practically confined to our mountain regions, 
where the conditions are unsuitable for agricultural purposes. 
We have now mentioned some of the metamorphic rocks 
which naturally tend to yield good soils. There are a con- 
siderable number of the same group of rocks, however, which 
from their mineralogical composition could not be expected 
to supply fertile soils. Amongst these may be mentioned 
clay-slate, over which the soil is usually a cold, wet, sterile 
clay. Now and again, however, owing chiefly to the presence 
in the slate of felspathic and micaceous ingredients, the soil 
may be of somewhat better quality. Another very unfavour- 
able rock is guartsite, the thin soil formed upon which 
consists chiefly of chips, splinters, and grains of the rock 
held together sometimes by a meagre ferruginous sand. 
Serpentine, composed of a somewhat intractable or relatively 
insoluble hydrous magnesian silicate, is not more favourable 
to the production of soil than quartzite, the thin soil yielded 
by it being notable for its infertility. 
Between these relatively barren soils and the good soils 
which, under favourable conditions, tend to form upon gneiss, 
mica-schist, and amphibolites, there are soils of intermediate 
character met with in many regions of metamorphic rocks ; 
such as those that occur above granulite, marble, chlorite- 
schist, etc. The soils in question necessarily vary much in 
character, for the mineralogical composition of the rocks 
themselves is by no means uniform. The soil overlying 
marble is usually a clay (coloured red, brown, or yellowish, 
from the presence of iron-oxide), which may contain little or 
no trace of calcium carbonate. Marble, however, is "igs 
infrequently charged with many “new” or “contact-minerals,” 
such as amphiboles and micas, from the gradual decomposi- 
tion of which in subsoil and soil carbonates of lime and 
magnesia may be derived. Granulite, on the other hand, 

