BOOK XVII. II. 24-111. 27
that we have specified like shade and even cold. Consequently the best course is to rely on experiment.
Soils favourable for trees, vines, and crops. XVI. 74.III. It comes next after the heavens to give an account of the earth, a subject no easier to deal with, inasmuch as the same land is not as a rule suited for trees and for crops, and the black earth of the kind that exists in Campania is not the best soil for vines everywhere, nor is a soil that emits thin clouds of vapour, nor the red earth that many writers have praised. The chalky soil in the territory of Alba Pompeia and a clay soil are preferred to all the other kinds for vines, although they are very rich, a quality to which exception is made in the case of that class of plants. Conversely the white sand in the Ticino district, and the black sand found in many places, and likewise red sand, even when intermingled with rich soil, are unproductive. The signs adduced in judging soil are often misleading. A soil in which lofty trees do brilliantly is not invariably favourable except for Those trees: for what grows higher than a silver fir? yet what other tree could have lived in the same place? Nor do luxuriant pastures always indicate a rich soil: for what is more famous than the pastures of Germany? but immediately underneath a very thin skin of turf there is sand. And land where plants grow high is not always damp, any more, I protest, than soil that sticks to the fingers is always rich—a fact that is proved in the case of clay soils. In point of fact no soil when put back into the holes out of which it is dug completely fills them, so as to make it possible to detect a close soil and a loose soil in this manner; and all soil covers iron with rust.a Nor can a heavythe land will be suitable for grazing and for vineyards, but if it more than fills it the soil will do for heavy arable land.
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