INTERACTION OF THE SPHERES 17 



vided into the three phases : Erosion, Transportation, and Dcposi- 

 fion. Erosion consists of Clastation,'^ or the breaking- up of the rock- 

 masses in situ; and Ablation, or the separation of material from the 

 main mass. The first process is accompHshed to a large extent 

 by atmospheric forces and hence is called weathering. It affects 

 only the upper zone of the earth's crust, which is termed the 

 zone or belt of ^vcathcring, while the zone beneath it is termed the 

 belt of cementation. The processes of erosion may be tabulated as 

 follows: (8; 34o7J-) 



EROSION. 



I. Clastation (breaking up of rock material). 



A. Physical or Disintegration. 



1. Atmospheric (generally included under weather- 



ing). 



a. Insolation and radiation. 



b. Frost shattering. 



c. Electrical (lightning) shattering, etc. 



2. Hydrospheric, w-ave shattering, etc. 



3. Pyrospheric, shattering by volcanic explosion. 



4. Centrospheric, shattering by earthquakes. 



5. Biospheric, shattering by growing organisms, by 



man, etc. 



B. Chemical or Decomposition. 



1. Atmospheric (weathering in the narrower sense; 



oxidation, hydration, carbonation. etc.). 



2. Hydrospheric (hydration, oxidation, etc.). 



3. Pyrospheric (decomposition through the activities 



of eruptive masses; of fumaroles, etc.). 



4. Biospheric (decomposition under influence of liv- 



ing matter, probably rare.) 

 II. Adlation (separating off, or removal of material). 

 A. Mechanical. 



I. Denudation, removal of weathered or loose ma- 

 terial, /. e., mantle rock. 



a. by wind = deflation. 



b. by streams = fluvial ablation. 



c. by glaciers = exaration. 



d. by waves, shore currents, etc. 



e. by organisms. 



* From Gr. KXaa-rSs = broken, and atio7t. 



