78 ANIMAL LIFE AS A GEOLOGICAL AGENCY. 



AH tlie operations of rural liusbandry are destructive to spon 

 taneous 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 con- 

 quests. These unbidden and hungry guests — the gipsies of the 

 vegetable world — often have great aptitude for accommodation 

 and acchmation, 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 Northwestern prairies, have been so nearly extirpated by 

 the inroads of haK-wild vegetables which have come in the train 

 of the Eastern immigrant, that there is reason to fear that, in a 

 few years, his Tierbarium will constitute the only evidence of 

 their former existence.* 



There are plants — themselves perhaps sometimes stragglers 

 from their proper habitat — ^which are found only in small num- 

 bers and in few localities. These are eagerly sought by the bot- 

 anist, and some such species are believed to be on the very verge 

 of extinction, from the zeal of collectors. 



Animal Life as a Geological am^d 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 

 i covering whole provinces, and builds up from the depths of the 

 V 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 pro- 



the profits of the sulphur mines. Flour of sulphur is applied to the vine as a 

 remedy against the disease, and the operation is repeated from two to three or 

 four — and sometimes even eight or ten — times in a season. Hence there is a 

 great demand for sulphur in all the vine-growing countries of Europe, and 

 "Waltershausen estimates the annual consumption of that mineral for this sin- 

 gle purpose at 850,000 centner, or more than forty thousand tons. The price 

 of sulphur has risen in about the same proportion as that of wine. — Walter- 

 BHAU8EN, Ueber den SicilianiscJien Ackerbau, pp. 19, 20. 

 * Report of Commissioner of Agriculture of the United States for 1870. 



