FaiTnivg of Cornicall. 
409 
sea.'"* These accumulations are termed sedimentary ash (pro- 
vincially dun stone; or when blisterj', honeycomb dun). Their 
j)resence amonsf the slates is a certain evidence of the fertility of 
the soil. In districts where these al)ound are discovered beds of 
f/reenstone and other solid trapjjean rocks, " which seem to have 
formed sheets or streams of melted roclv.f amid the mud, silt, 
sand, or gravel then in the course of accumulation, and which now 
constitute associated beds of slate, sandstone, and conglomerates."]; 
Wherever these products of fire are discovered, the soil proves 
exceedingly productive. Again, in other portions of the slates we 
have accumulations of calcareous matters, and although never in 
sufficient breadth to give a character to the soil, yet they also are 
certain evidences of fertility. It is also observed, that the cha- 
racter of the soil on the slates is affected by their inclination or 
dip. Where the underlie is considerable and the subsoil shallow, 
the surface-soil is light and hungry, the soluble manures passing 
rapidly through the slaty fissures : and even where the stoes lie 
horizontally, and are of an indurated character, with the soil of 
little depth, such land will scorch or burn readily in the summer. 
We have a great deal of cliff-land of this description (26). § 
15. With these preliminary remarks I commence my survey 
of the soils on the slate district, which will be found to vary very 
considerably as respects their depth, texture, and fertility, these 
depending on the degree of mechanical division of the rocks, and 
their relative chemical elements, allowance being made always for 
the varied meteorological conditions to which they are exposed. 
This must not be lost sight of ; tlie central granite ridge of hills, 
which has been already described, exercises a very considerable 
influence on the meteorological conditions of the different parts of 
the county. On the northern side of the ridge, at the eastern ex- 
tremity, the effect of the winds from the Atlantic is very perceptible 
in the few trees which are exposed to their fui'y, and which grow 
with an inclination towards the opposite direction ; whilst on the 
south-east side the climate is as mild as the south coast of Devon, 
of which it is a continuation, and with a difference of latitude not 
* De la Beche. 
+ The intrusion of dykes and irregular beds of volcanic matter into the 
slate rock in the form of greenstone, serpentine, porphyry, and granite, 
is plainly seen throughout the whole of the county. 
% De'la Beche. 
§ It is generally considered that at the junction of the granite and 
slates the soil is improved by the niixtuie. This is no doubt true as far as 
Penzance and a few other places are concerned, where the greenstones 
prevail ; but instead of its being a general case, we have more commonly 
found quite the contrary effect produced from the indurated and altered 
state of the different slates at the line of junction, pioducin<r frequently 
a sterile effect. 
