CONSTRUCTION OF THE EARTH. 123 



ing to a large extent from material provided by organic 

 agencies that is, by the agency of animals and vegeta- 

 bles, especially the former. For example, the carbonate 

 of lime that is dissolved in water is taken up by animals 

 coral animals, shell-fish, etc., and, forming their frame- 

 work their skeleton, as we may term it is afterward 

 deposited as mineral matter, becoming again, as it was 

 originally, a part of the solid substance of the crust of 

 the earth. 



208. Alterations made by Man. Wherever man fixes 

 his habitation he effects more or less of change in the 

 earth's surface. These changes are especially manifest 

 in cities where large bodies of men are congregated. 

 Here levels are often considerably altered, as may be 

 learned from the recollections of the oldest inhabitants. 

 But all the changes produced by man are almost as 

 nothing compared with those which come from the op- 

 erations of the natural causes that I have noticed in this 

 chapter. 



CHAPTER XI. 



CONSTRUCTION OF THE EARTH. 



209. Stages in the Construction of the Earth. You will 

 see, in the developments which I shall make in this and 

 the succeeding chapters, that there has been a succession 

 of changes, each one occupying a long period of time, 

 the earth being brought gradually into a proper condi- 

 tion as a habitation for man. You will see that the con- 

 tinents were once mere germs of continents, and that 

 they grew to be what they are after a manifest plan, the 

 steps of which the geologist has been able to some ex- 

 tent to discover by his researches among the rocks. You 

 will see that during all this time there was much of tear- 

 ing down and rebuilding as a part of the plan, the sedi- 



