~ Parr Il. Sucr. iii. § 4.] MAN’S ACTION IN GEOLOGY. 471 
§ 4. Man as a Geological Agent. 
No survey of the geological workings of plant and animal life 
upon the surface of the globe can be complete which does not take 
account of the influence of man—an influence of an enormous and 
increasing consequence in physical geography ; for man has introduced, 
as it were, an element of antagonism to nature. Not content with 
gathering the fruits and capturing the animals which she has offered 
for his sustenance, he has, with advancing civilization, engaged in a 
contest to subdue the earth and possess it. His warfare indeed has 
often been a blind one, successful for the moment, but leading to 
sure and sad disaster. He has, for instance, stripped off the woodland 
from many a region of hill and mountain, gaining his immediate 
object in the possession of their stores of timber, but thereby laying 
bare the slopes to parching droughts or fierce rains. Countries once 
rich in beauty, and plenteous in all that was needful for his support, 
are now burnt and barren, or washed bare of their soil. It is only in 
comparatively recent years that he has learnt the truth of the 
aphorism—*“ Homo Nature nunister et interpres.” 
But now, when that truth is coming more and more to be recog- 
nized and acted on, man’s influence is none the less marked. His 
object still is to subdue the earth, and he attains it, not by setting 
nature and her laws at defiance, but by enlisting her in his service. 
Within the compass of this volume it is impossible to give more than 
merely a brief outline of so vast a subject... The action of man is 
necessarily confined mainly to the land, though it has also to some 
extent influenced the marine fauna. It may be witnessed on climate, 
on the flow of water, on the character of the terrestrial surface, and 
on the distribution of life. 
1. On Climate.—Human interference affects meteorological 
conditions—(1) by removing forests and laying bare to the sun and 
winds areas which were previously kept cool and damp under trees, 
or which, lying on the lee side, were protected from tempests; as 
already stated, it is supposed that the wholesale destruction of the 
woodlands formerly existing in countries bordering the Mediter- 
ranean has been in part the cause of the present desiccation of these 
districts; (2) by drainage, the effect of this operation being to 
remove rapidly the discharged rainfall, to raise the temperature of 
the soil, to lessen the evaporation, and thereby to diminish the rain- 
fall and-somewhat increase the general temperature of a country ; 
(3) by the other processes of agriculture, such as the transformation 
1 See Marsh’s ‘‘ Man and Nature,” a work which, as its title denotes, specially treats 
‘of this subject, and of which a new and enlarged edition was published in 1874 under 
the title of “ The Earth as modified by Human Action.” It contains a copious biblio- 
graphy. See also Rolleston, Jour. Itoy. Geog: Soc. xlix. p. 320, and works cited by him, 
particularly De Candolle, “Géographie botanique raisonnée,”’ 1855; Unger’s “ Botanische 
Streifziige,” in Sitzber. Vienna Acad. 1857-1859; J. G. St. Hilaire, “ Histoire naturelle 
générale des Regnes Organiques,” tom. iii. 1862 ; Oscar Peschel, “ Physische Erdkunde ; ” 
Link, “ Urwelt und Alterthum ” (1822). 
