Farming of CormcaV. 
405 
but siliceous sand and gravel. The following are two analyses of 
granite,* assuming No. 1 to be composed of | felspar, | quartz, 
mica ; No. 2 of | quartz, ^ mica, | felspar : — 
No. 1. No. 2. 
Silica . . . 13-04 74-84 
Alumina . . . 18-83 12-80 
Potash . . . 8-51 '7-48 
Magnesia . . . O'SS 0-99 
Lime . . . 0-44 0-37 
Oxide of Iron . . 1-73 1-93 
0.xiile of Manganese . 'O-IO 0 12 
Fluoric Acid " . . 0-18 0 21 
The presence of iron also exerts a considerable influence on 
the " growan " soils, tending to their improvement, whilst schorl, 
which pervades a great manv of the granites, tends when in excess to 
impair them. In the hollows or levels where natural drainage does 
not exist, stiff clay-soils prevail, which are often cold and unfruit- 
ful, but are capable of amelioration where the depth of surface- 
soil is sufficient, bv draining and proper cultivation. The growan 
soil is black, and the subsoil frequently of great depth and of a 
yellowish colour. 
8. Commencing our survey of the granite soils at the eastern 
extremity, being the entrance to the county from the Devonshire 
side, the reader will be conveyed ideally over a ridge of bare and 
rugged rocks, running through the whole length of the county, 
from Launceston to the Land's End : the commencement exhibiting 
the appearance of a dreary waste, and forming by far the most 
uninviting part of the journey. In the map.f four insulated 
''outbursts" will be seen, coloured red, which form this central 
ridge. 
9. The Roughtor district 1^. is about 10 miles in length and 
6 or 7 in breadth — 8794 acres of which are uncultivated waste. 
The cultivated portion, where the natural drainage is good, is 
parcelled out in small farms, let from 10s. to 15s. per acre. In 
the parish of Advent some are let as high as 20s. There is also 
a great breadth of land enclosed, forming rough pasture, let from 
2s. to 3s. 6rf. per acre. Oats and wheat are chiefly grown, aver- 
* Sir H .T. De la Beche, F.R.S., &c., p. 449, ' Manual of Geology.' 
■;• The map which accompanies this Report is a fac-simile of Sir H. T. 
De la Beche's index-map to the geological survey of Cornwall. It may 
be regarded as a true map of the soil, since there is no county in England 
where there is a gieater relation between the soils and the subjacent rocks. 
The sections will also convey to the mind of a stranger the mode in which 
the various strata intersect each other. 
% Ascertained by Mr. Stephens of Hengar, St. Tudy, for the purpose of 
this Report. 
