6i 
OF CORNWALL. 
Dr. Plot h is fond of attributing the fertility of earth to the warm 
fleams arifing from metals and minerals below ; but the fterility ( 
may be great, where metals and minerals abound, of which no place 1 
perhaps affords more frequent inftances than Cornwall ; for here the 
coarfeft grounds abound moft in metals, and on the other hand, 
there is the greateft plenty of corn, grafs, plants and trees, where 
no metals or minerals have ever appeared. 
To aflign any one general caufe of the fertility of the earth, 
would be to build upon too narrow a bottom ; one of the greateft 
prodigies oi nature is, that earth fliould aftiime fo many fhapes, and 
nourifh, and conftitute fuch a variety of bodies : we know by ex- 
perience, that many materials muft concur, and that fome are more 
prolific than others, but by what procefs, earth is transformed into 
nourifhment, we cannot fo much as guefs. Earth is the general 
food and J} amen oi all bodies, yet of itfelf we know it can do no- 
thing ; it muft be connected by a cement, or it cannot form ftone ; 
it muft be loftened and attenuated by moifture and warmth, or 
it cannot enter into the alimentary veftels of plants and animals. By 
experiment indeed, it appears, that the confumption of that Earth, 
in which trees are planted, is not great, nor at all proportionable to 
the perfpiration and increaftng bulk of thofe trees * ; yet muft not 
Earth be denied its due fhare in vegetation ; the parts of Earth 
which conftitute the folids of any plants are extremely fine, and 
all the water we pour, or rain that falls on plants, is well flocked 
with thofe fine, earthy parts, now the common mafs in which we 
plant trees, is for the moft part Gravel, Clay, and Sand, which 
piomote vegetation, but are too grofs to enter into, and become 
the conftituent parts of plants, and therefore cannot much decreafe 
in weight or bulk : water muft therefore be confidered as the vehicle 
of more folid nourifhment, and the parent of the fluids : the earths, 
falts, and oils, are the great inftruments of the increafe of folids. To 
trace fertility a little farther : When the earth is foftened and diluted, 
heat rarefies and evaporates the mixture; the falts contained and 
diflolved, are always active, and promote motion ; the elafticity of 
the air quickens and continues it ; the oils fupple the paflages, of 
which fome, are ntted to fecrete, arreft, and depofit the nutritious 
particles as they pals ; fome adapted ( by the fame fecret hand which 
conducts every part oi the operation) to throw off the redundant 
moifture by perfpiration : the more earthy mixture compotes the 
haid and folid parts, and the genial, little atmofphere of every 
plant gives fpirit, colour, odour, and tafte. Herbs and fruit, being 
thus led and maturated, make the earth they contain better pre- 
h Oxfordshire, page 57, 58, &c. > Dr. Hales’s Vegetable Statics. 
