CHAPTER VII 



RECONSTRUCTIVE PROCESSES — LAND, SWAMP, AND RIVER 



DEPOSITS 



We have now to inquire what becomes of the material derived 

 from the mechanical and chemical disintegration of the rocks, for 

 it is not destroyed, but only changed. Most of it is eventually 

 carried to the sea and there deposited ; but even on the land, and 

 in lakes and rivers, a certain proportion of the waste finds a rest- 

 ing place for a longer or shorter period of time. While the rocks 

 which form the accessible crust of the earth are, for the most 

 part, of marine origin, yet those formed in other ways have great 

 geological significance, because of the assistance that they give 

 in the determination of ancient land surfaces, lake beds, river 

 channels, ice fields, and the like. Hence it becomes necessary 

 to study all the methods by which rock reconstruction is per- 

 formed, on however small a scale. 



I. Terrestrial Deposits 



Under this head are included all those accumulations of the 

 mechanical and chemical waste of preexisting rocks, which are 

 formed on land surfaces and not in bodies of water. Deposits 

 made by ice, on land or under water, will be considered in a 

 separate section. 



Soil. — The crumbling remnant of disintegrated rocks forms 

 soil, which under the influence of wind, rain, frost, and other agen- 

 cies, is travelling down the slopes, accumulating, often to great 

 thickness, in depressions and valleys. Very little soil, as such, is 

 permanently built into the earth, by far the greater part of it 

 reaching the sea and being sorted and deposited there. Some- 



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