54 THE KINDS OF EOCKS 



constituents. In structure massive, crystalline, or glassy, or in 

 certain altered forms, colloidal. 



II. Aqueous Rocks. — Eoeks formed mainly through the 

 agency of water, as (-4.) chemical precipitates or as {B) sedi- 

 mentary beds. Having one or many essential constituents. In 

 structure laminated or bedded; crystalline, colloidal, or f rag- 

 mental; never glassy. 



III. ^olian Rocks. — Eocks formed from wind-drifted ma- 

 terials. In structure irregularly bedded ; f ragmental. 



IV. Metamorphic Rocks. — Rocks changed from their orig- 

 inal condition through dynamic or chemical agencies and which 

 may have been in part of aqueous, seolian, or of igneous origin. 

 Having one or many essential constituents. In structure bedded, 

 schistose or foliated, crystalline or colloidal. 



