EXOGENETIC ROCKS 289 



Sherzer designates as subtypes sands of one type modified by 

 another agency and calls them by a compound term. Thus an 

 aqueo-residual sand (hydro-atmoclastic sand) is one in which the 

 granules have been produced by the various residual agencies, and 

 are subsequently more or less modified by water action. Again a 

 residuo-aqueous sand (atmo-hydroclastic) is one in which water- 

 rounded grains have been subjected to the agencies of weathering, 

 and give more or less evidence of such action. The principal sub- 

 types or intermediate types may be grouped as follows : 



aeolo-aqueous or anemohydroclastic 

 aeolo-residual or anemoatmoclastic 

 seolo-volcanic or anemopyroclastic 

 aeolo-glacial, etc. or anemoautoclastic 

 aqueo-seolian or hydroanenioclastic 

 aqueo-residual or hydroatmoclastic 

 aqueo-volcanic or hydropyroclastic 

 aqueo-glacial, etc. or hydroautoclastic 

 residuo-aeolian or atmoanemoclastic 

 residuo-aqueous or atmohydroclastic 

 residuo-volcanic or atmopyroclastic 

 residuo-glacial or atmoautoclastic 

 glacio-aeolian or auto-anemoclastic 

 glacio-aqueous or auto-liydroclastic 

 glacio-residual or auto-atmoclastic 

 glacio-volcanic or auto-pyroclastic 



In all cases the agent last modifying the type is placed first, the 

 agent producing the original type last. The organic elastics or bio- 

 clastics are of such recent origin that reworking by other agents has 

 not occurred on an extensive scale. When it occurs, the coupling 

 of the respective prefix with bioclastic will designate it. Reworking 

 of other sands by volcanic agencies is of so rare an occurrence that 

 such types may be neglected, although in a complete classification 

 they must be included. 



The organic (biogenic) and concentration or chemical (hydro- 

 genic) sand types may also be reworked, producing seoloorganic 

 and seolo-concentration types, aqueo-organic and aqueo-concentra- 

 tion types, etc. — i. e., the wind- or water-worn and the weathered 

 biogenic and hydrogenic sands. The characters of the undisturbed 

 endogenetic sands will be more fully dealt with in later chapters. 

 The principles of classification applied to sands may equally be ap- 

 plied to the coarser or rudaceous material and the finer or lutaceous 

 matter. 



