The Soil 



earth, as we have shown by the case of the high moun- 

 tain where the decreased pressure allows rapid radiation. 

 Professor King, in his book on the soil, quotes the work 

 of Professor Langley, who, " after making a long and very 

 careful experimental study of this property of our atmos- 

 phere, at the base and summit of Mt. Whitney, in Cali- 

 fornia, reached the conclusion that, had our earth no 

 atmosphere, its surface temperature, even at the equator 

 at noon, would be 200 degrees C. below freezing, or 

 —328 F." The radiation of heat from the earth is always 

 greater in cloudless weather, and on bright moonhght 

 nights in spring we are apt to have killing frosts, not 

 because of the moon, but because of the clear atmos- 

 phere at such times. 



One of the most active agents in the trans- 



\^3.tCr £LS £L 



Soil Builder formation of the original rocks into soil is 

 water. We can to-day study its continual 

 work by merely examining the hills and roadsides after a 

 heavy rain and noting the transportation of the soil from 

 higher to lower levels. In connection with water the 

 frost has been one of the most efficient agents in breaking 

 down the rocks. Water getting into the small crevices of 

 the rocks freezes, and by its expansive force breaks off 

 the particles which the rain washes down. In this way 

 every exposed rock is still made to contribute slowly to 

 the soil below. 



When life began upon the earth there evidently must 

 have been vegetation of some sort, since vegetation is 

 essential to animal life. We find that even in the oldest 

 rocks now known, rocks that have been transformed by 

 heat, and which hence contain no animal or vegetable 



