The Earth as Modified by Human Action eBook

All the operations of rural husbandry are destructive to spontaneous vegetation by the voluntary substitution of domestic for wild plants, and, as we have seen, the armies of the colonist are attended by troops of irregular and unrecognized camp-followers, which soon establish and propagate themselves over the new conquests.  These unbidden and hungry guests—­the gipsies of the vegetable world—­often have great aptitude for accommodation and acclimation, and sometimes even crowd out the native growth to make room for themselves.  The botanist Latham informs us that indigenous flowering plants, once abundant on the North-Western prairies, have been so nearly extirpated by the inroads of half-wild vegetables which have come in the train of the Eastern immigrant, that there is reason to fear that, in a few years, his herbarium will constitute the only evidence of their former existence. [Footnote:  Report of Commissioner of Agriculture of the United States for 1870.]

There are plants—­themselves perhaps sometimes stragglers from their proper habitat—­which are found only in small numbers and in few localities.  These are eagerly sought by the botanist, and some such species are believed to be on the very verge of extinction, from the zeal of collectors.

ANIMAL LIFE AS A GEOLOGICAL AND GEOGRAPHICAL AGENCY.

The quantitative value of animated life, as a geological agency, seems to be inversely as the volume of the individual organism; for nature supplies by numbers what is wanting in the bulk of the animal out of whose remains or structures she forms strata covering whole provinces, and builds up from the depths of the sea large islands, if not continents.  There are, it is true, near the mouths of the great Siberian rivers which empty themselves into the Polar Sea, drift islands composed, in an incredibly large proportion, of the bones and tusks of elephants, mastodons, and other huge pachyderms, and many extensive caves in various parts of the world are half filled with the skeletons of quadrupeds, sometimes lying loose in the earth, sometimes cemented together into an osseous breccia by a calcareous deposit or other binding material.  These remains of large animals, though found in comparatively late formations, generally belong to extinct species, and their modern congeners or representatives do not exist in sufficient numbers to be of sensible importance in geology or in geography by the mere mass of their skeletons. [Footnote:  Could the bones and other relics of the domestic quadrupeds destroyed by disease or slaughtered for human use in civilized countries be collected into large deposits, as obscure causes have gathered together those of extinct animals, they would soon form aggregations which might almost be called mountains.  There were in the United States, in 1870, as we shall see hereafter, nearly one hundred millions of horses, black cattle, sheep, and swine.