296 



PRINCIPLES OF STRATIGRAPHY 



in the lutaceous and arenaceous types, but the rudaceous sediments 

 of fluvio-clastic origin may often be distinguished from those of 

 wave-laid origin by minor characters of the component material. 

 Thus exceedingly well-rounded boulders of moderate size are more 

 characteristic of river than of wave work. The remarkable percus- 

 sion or shatter marks {Schlagnarhcn) found on fine-grained boul- 

 ders transported by torrents are further to be noted. They consist 

 of semicircular or crescent-shaped slits, appearing as if made by a 

 thumb nail, and crossing each other or interlocking in an indeter- 

 minate manner. They are due to a sudden blow upon the smooth 

 surface from a rounded pebble or boulder of equally hard rock. 

 6. The Bioclastics. These are the clastic rocks which owe 

 their essential character to organisms. The only class of 

 great importance is that for which man is responsible. Thus 

 bricks (as material), plaster, concrete, cement, etc., are no 

 mean portion of the material composing the uppermost lay- 

 ers of the earth's crust, and are all to be included with the 

 bioclastic division of rocks. 



I 1 



Summary of "Sedimentary Rocks." 



The following table shows the more familiar types of "sedi- 

 mentary" rocks, with the more important species included under 

 each : 



r Hydrorudytes 

 \ Hydrosilicirudytes 

 Hydrocalcirudytes 



Pyrorudytes (agglomerates) 



Autorudytes 



Autosilicirudytes 



Autocalcirudytes 



Atmorudytes 



Atmosilicirudytes 



Atmocalcirudytes 



Biorudytes (artificial rubble rock) 



' Autoarenytes 



Autosilicarenytes 



Atmosilicarenytes 



Anemosilicarenytes 



Hydrarenytes 



Hydrosilicarenytes 

 . Bioarenytes (artificial sandstones} 



I. Conglomerates 

 or 

 Puddingstones. 



2. Breccias. 



Sandstones. 



