SCENERY, SOIL AND THE ATMOSPHERE 573 



Britain and the North Sea, or the ice fields of Greenland with the 

 ample life of Scandinavia, if we wonder at the small part which latitude 

 seems to have with opposite shores of the Atlantic, we are at once led 

 back to the atmosphere for light upon our problem. 



Likewise for all life, the atmospheric gases are essential as a heat 

 regulator and in the employment of their substances for organic struc- 

 tures. Through these structures, in turn, all soil-making is profoundly 

 conditioned, and those organic accumulations are made possible, which 

 we find in the mineral fuels and in most limestones. 



If we turn to the direct work of the atmosphere, we shall find a 

 group of facts, not so conspicuous, perhaps, but worldwide and impor- 

 tant. This is one of the newer subjects in geology, and to consult any 

 text-book written twenty years ago would yield a scant result in 

 information. 



The atmosphere is the agent of incessant chemical change, the world 

 over, and down to the level of the ground water. Whether the water 

 table be found close to the surface or far down, the atmosphere finds 

 access to some parts of the rocks down to that horizon. The depth 

 below the surface depends on the water supply, on the character of the 

 rocks and on the surface topography, and it is different in the same 

 place at different times, but always and everywhere the gases that sur- 

 round and surmount us, are pursuing their underground activities as 

 well. And it is scarcely proper to limit them to zones above the water 

 table, for they communicate some measure of their efficiency to the 

 ground waters, which in turn may go far down, and may make long 

 journeys before they emerge, thus giving the atmosphere some share in 

 the segregation of those metallic substances which belong in the inven- 

 tory of the world's wealth. 



The making of soil is a complicated process, or bundle of processes. 

 Fundamentally it is due to the breaking down of rocks, and this is 

 effected by change of temperature, by organisms, by the wear of running 

 streams, glaciers and ocean waves. But when the rocks are broken 

 down, processes more intimate and essential must be added. These 

 more intimate agencies are the water, the atmosphere and decaying 

 organisms. The water will accomplish solution and thus make certain 

 minerals available for the nutrition of crops. But the water falling as 

 rain has gathered from the atmosphere minute portions of its carbon 

 dioxide, and has become thereby an effective dissolving agent. Most 

 rocks contain more or less iron in a disseminated condition. The 

 oxygen of the air combines readily with this metal, promoting the decay 

 of the rock mass, and coloring not only the rock, but the soils that ulti- 

 mately come into being. When the farmer selects a field to lie fallow 

 he stirs the soil, gives it all possible exposure to air, water and heat, and 

 thus speeds these silent processes which go on in some measure every- 

 where, with or without his ken. It is the time required to produce 



