THE GEOLOGY OF ORKNEY. lxxiil 
flagstones so calcareous that they have been burned 
for lime, but there are no pure limestones in the Old 
Red Sandstone of Orkney. Other flagstones consist 
so largely of clay that they might be described as 
dark shales, but they are not laminated. In the face 
of the cliffs the hard sandy beds weather out as 
prominent bands, while the soft shales or “calm- 
stones” are eaten back by the weather and form 
recesses. Beds which contain much carbonate of 
lime are comparatively rare. 
SOIL FORMATION. 
Where the flagstone beds weather they are readily 
broken up by the frost, because their bedding is ex- 
ceedingly perfect, and they are also traversed by 
numerous joints. The subsoil in such a case is a 
rubble of loose rock fragments embedded in a fine 
brownish clay that represents the most weathered 
part of the subjacent rock. Although the soil is 
clayey it is well drained, and there is little tendency 
for water to be held up at the surface. The flagstones 
also are often sandy, and always somewhat calcareous ; 
they contain phosphates, both in mineralized state (as 
apatite), and as the teeth, scales and bones of fishes. 
Hence the soil is of mixed character, and may be 
described as a clayey loam, not devoid of lime, and 
fairly well provided with potash and phosphates. 
Although not a rich soil, it is by no means a sterile 
one. Soils of this kind are to be found over a large 
part of the county, especially at moderate elevations, 
where there is no great surface accumulation of boulder- 
clay or alluvium. At the highest elevations ee flag- 
