Agriculture of the Scilhj Isles. 
377 
usually a somewhat coarse compound of quartz, felspar, and mica, 
both dark-coloured and silvery, and a finer-grained granite is 
not unfrequently detected in it in the form of veins."* 
The rock is remarkably loose in texture, readily disintegrating, 
and liable to rapid decomposition. It is much jointed, especially 
at the surface. This favours disintegration. " At Watermill 
Bay the joints are so close to each other, and so highly inclined, 
as to give to the whole mass the appearance of stratified granite."! 
Dr. Paris, to account for the fertility of the soil at Scilly, 
mentions the presence in the granite of large quantities of iron 
and felspar. These constituents would, as he justly remarks, 
induce speedy decomposition.^ The grey granite is the prevalent 
variety. The red is present in much smaller quantity. The sand 
in some of the bays is very micaceous. 
Soil. — The soil varies from an almost pure sand to a dark 
sandy loam, and is very free from stones. Woodley tells us that 
" the vegetable soil is a black peat, intermingled with granitulous 
particles, and known in Cornwall by the name of grovvan or 
gritty. This stratum is about 2 feet in depth, becoming of a 
lighter and greyish colour in proportion to its distance from the 
surface. Next to this is a yellowish loamy clay, found in a 
stratum of 5 or 6 feet in depth, and intermingled with stones. 
The colour of the clay becomes darker, and the stones imbedded 
in it are larger, in proportion to their depth from the surface. 
Under the whole are found large masses of granite rock, fit for 
building and other purposes. "§ 
This description is not altogether correct ; for the soil, con- 
sidered as a Avhole, is not a black peat, though it may, in some 
districts, be of that nature. Nor did our observation confirm the 
statement in regard to the " yellowish loamy clay." We heard, 
indeed, of a clay subsoil in one locality ; and, in all probability, 
it is present in other parts, but it is not generally distributed. 
The soil is more sandy, and consequently lighter, on St. Martin's 
and St. Agnes than on Tresco and St. Mary's. Its depth varies 
very much. 
All the islands contain many acres of waste land or downs, 
more or less studded with masses of rock, among which may be 
found a scanty herbage of poor short grass, ferns, and heath, and 
several clumps of strong-growing furze. 
On St. Mary's there is a limited area of marshy land. 
* ' Report on the Geology of Cornwall, Devon, and West Somerset,' by Henry 
T. de la Beche, F.R.S (1839). 
t From a Paper read before the Royal Geological Society of Corn-wall, Septem- 
ber, 1850. 
i ' Transactions of Royal Geological Society of Cornwall,' vol. i. (1818). 
§ Woodley on the Scilly Isles (1S22). 
