1546 ; the second at Basel, 1558, which, being the edition revised and added to
by the author, has been used by us for reference. There are five " books," and
in the main they contain Agricola's philosophical views on geologic phenomena.
The largest portion of the actual text is occupied with refutations of the
ancient philosophers, the alchemists, and the astrologers ; and these portions,
while they exhibit his ability in observation and in dialectics, make but dull
reading. Those sections of the book which contain his own views, however,
are of the utmost importance in the history of science, and we reproduce
extensively the material relating to ore deposits in the footnotes on pages 43
to 52. Briefly, Book I. is devoted to discussion of the origin and distribution
of ground waters and juices. The latter part of this book and a portion of
Book II. are devoted to the origin of subterranean heat, which he assumes
is in the main due to burning bitumen—a genus which with him embraced
coal—and also, in a minor degree, to friction of internal winds and to
burning sulphur. The remainder of Book II. is mainly devoted to the discussion of subterranean " air", " vapour", and " exhalations", and he conceives that volcanic eruptions and earthquakes are due to their agency, and
in these hypotheses he comes fairly close to the modern theory of eruptions
from explosions of steam. " Vapour arises when the internal heat of the
" earth or some hidden fire burns earth which is moistened with vapour.
" When heat or subterranean fire meets with a great force of vapour which
" cold has contracted and encompassed in every direction, then the vapour,
" finding no outlet, tries to break through whatever is nearest to it, in order
" to give place to the insistent and urgent cold. Heat and cold cannot abide
" together in one place, but expel and drive each other out of it by turns".
As he was, we believe, the first to recognise the fundamental agencies
of mountain sculpture, we consider it is of sufficient interest to warrant a
reproduction of his views on this subject : " Hills and mountains are pro" duced by two forces, one of which is the power of water, and the other the
" strength of the wind. There are three forces which loosen and demolish
" the mountains, for in this case, to the power of the water and the strength
" of the wind we must add the fire in the interior of the earth. Now we can
" plainly see that a great abundance of water produces mountains, for the
" torrents first of all wash out the soft earth, next carry away the harder
" earth, and then roll down the rocks, and thus in a few years they excavate
" the plains or slopes to a considerable depth ; this may be noticed in moun" tainous regions even by unskilled observers. By such excavation to a
" great depth through many ages, there rises an immense eminence on each
" side. When an eminence has thus arisen, the earth rolls down, loosened by
" constant rain and split away by frost, and the rocks, unless they are exceed" ingly firm, since their seams are similarly softened by the damp, roll down
" into the excavations below. This continues until the steep eminence is
" changed into a slope. Each side of the excavation is said to be a mountain,
" just as the bottom is called a valley. Moreover, streams, and to a far greater
" extent rivers, effect the same results by their rushing and washing ; for this
" reason they are frequently seen flowing either between very high mountains
