Classification of Sediiitcnfary Rocks. — Grahaii. 
241 
which the essential character of the material is due to the me- 
chanical work of the water. Such a rock may still be consid- 
ered as bioclastic, but constituting a passage rock to the hydro- 
elastics. Again, bricks made from clay which itself is atmo- 
clastic, i.e. due to the disintegration of shales or of feldspathic 
rocks, serve to connect the atmoclastic and bioclastic groups. 
Diagram II.— T.ntekrklations of the Exoge.netic Rocks. 
A. B. C represents the crust of the earth. From v.-ithin the crust, but still 
external as far as the rocks are concerned, volcanic explosions produce the 
Pyroclastic rocks on the surface of the crust. Within the crust itself, the 
/I utoc/a.st;c rocks are formed, while from without, the Htniosphere, water, and 
organisms attack the crust, producing Atmoc/ast/c (including Anenioclastic), 
Hydroclastic, and Bioclastic rocks. The final result of the destructive work 
of the various agents, returns the material of the rocks either to the air, to the 
state of solution in water, or to a state of fusion. .\ part may remain as 
assimilated organic matter and be redeposited Iiiogenetically as new rock. 
The remainder will be redeposited from the various states to which it has been 
returned, by the corresponding endogenetic agents. 
The hydroclastic condition of rocks terminates in a state of 
solution, which is the ultimate degree of destruction water can 
effect. The atmosphere likewise may bring about solution by 
the aid of its vapors (corrosion), and so may organisms. So- 
lution then is one of the limiting stages of the clastic condition 
in cither atmo-, hvdro- or bio-clastic rocks. In the atmoclastic 
