200 



NATURE FOR ITS OWN SAKE 



the sedimental deposits ; doubtless, there were 

 at other times great streams of hot lava forced 

 up from below by volcanoes and spread over 

 vast surfaces, cementing the sedimental de- 

 posits into rock strata ; and doubtless, again, 

 chemical action and change by and through 

 air, water, fire, produced other rock masses 

 with which geology acquaints us. The forms of 

 rocks, their twisted, broken, or waving strata, 

 were caused by convulsions of the earth (either 

 expansions or contractions of the crust) which, 

 following the form of a wrinkle or a fold, have 

 heaved the surface in some places and depressed 

 it in other places. The deposits which we call 

 soil, together with the bowlders and loose 

 stones, are but the grit from rock formations, 

 broken away by frost, wind, and rain, and 

 washed down into the valleys by the brooks and 

 streams. 



The human being has always had a very keen 

 appreciation of the earth's volume and sub- 

 stance. Earthquakes may shake his house, but 

 not his faith. The tremor is but temporary ; he 

 still believes in the solidity of the earth under his 

 feet. And yet how seldom he thinks of the im- 

 mensity of the structure, its continuity, its long 

 endurance, factors which have made possible its 



