448                                              SILURIA.                                 [Chap. XIX.
 

CHAPTER XIX.

ON THE ORIGINAL INTRODUCTION OF GOLD INTO THE EARTH'S
CRUST AND ITS SUBSEQUENT DISTRIBUTION IN DEBRIS OVER
VARIOUS PARTS OF THE SURFACE.

Cojs^siDEEii^G the great quantity of Gold which has of late years been found
in California and Australia, it may be expected that an author who has
borne a part in the discussions upon this subject* should devote some
pages to so engrossing a topic,—the more so as my chief article of belief
has now proved to be true, viz. that the rocks which are the most aurife¬
rous belong to the Palaeozoic epochs, and especiaUy to the Lower-Silurian
age.    At the same time I have to modify to some extent that aphorism;
for it wUl be shown that there are examples of auriferous igneous rocks and
veinstones having been protruded into strata of Secondary age, the latter
having become to some extent auriferous,—a fact unknown to me when the
last edition of this work was published.    The views now put forth wiU
chiefly relate to the geological and mineralogical conditions under which
gold has occurred.    As a clear understanding of this point may tend, in
some measure, to aUay the fears of those who think that the metal may
be discovered over regions vastly more enormous than the tracts to which
it is restricted, certain geological and statistical data and arguments that
I have advanced in greater detaU in other works are here brought together.

Let us first reflect upon the general fact that, whilst aU the stratified
formations are composed either of crystaUine and Palaeozoic rocks or of
Secondary and Tertiary deposits, gold has never been found in any appre¬
ciable quantity in either of the two last-mentioned classes of strata where
they are in their natural state, i. e. where they have not been penetrated
by igneous rocks or metamorphosed and impregnated with mineral veins.
The vast areas, therefore, which are covered by all such younger unaltered
formations are excluded from the general auriferous area; and every one
who hves in tracts the subsoU of wliich consists of such unaltered rocks,
may at once be assuftd that he can never find gold in them.

Having laid down this generahzation, which affirms that by far the
largest countries contain Uttle or no gold, we proceed to consider the

* See ' Eussia-in-Europe and the Ural Moun-     18.50, vol. Ixxxvii., Article ' Siberia and California,'

tains,' p. 437 et seq.; Trans. K. Geogr. Soc, Pre-     p. 39.    Quart. Journ. Geol. Soc. Lond. vol. viii.

sident'a Discourses, vol. xiv. 1844-1845,—in the     p. 134.    And, lastly,  ' Further Papers   on the

first of which the Australian rocks were compared     Kecent Discovery of Gold in Australia,' presented

with those ofthe Ural.    Trans. Eoyal Geological     to Parliament Aug. 16, 1853, p. 43, including my

Society, Cornwall, 1846, p. 324 et seq., in which     correspondence, in 1848, -with Her Majesty's Se-

Cornish tin-miners were incited to emigrate and     cretary for the Colonies, on the then known exist-

work for gold in Australia.    Eeport of the British     ence of gold in Australia, and tendering my advice

Association for the Advancement of Science, 1849     as to the manner of opening out useful gold-works

(Trans, of Sections, p. 60).   Proceedings of the     in the Colony.
Eoyal Institution, March 1850, Quarterly Eeview,