STRUCTURE OF SEDIMENTARY ROCKS 



13 



tion of all the 

 older rocks and 

 from the inorganic 

 remains of plant 

 and animal life. 

 These comprise 

 clay and shale (ar- 

 gillaceous), sand- 

 stone, conglom- 

 erate and breccia 

 (aren aceous) ; 

 limestone and dol- 

 omite (calcare- 

 ous) , together with 

 minor rocks of vol- 

 canic, phosphatic 

 and carbonaceous 

 character. 



The sand- 

 stones, shales, 

 limestone and dol- 

 omite are easily 

 the most promi- 

 nent of this group, 

 and, in fact, of all 

 the types of rock, 

 in their present 

 agricultural im- 

 portance. They 

 compose immense 

 strata of rock, and 



Fig. 5. Photomicrograph of chert. (Lord.) 



Fig. 6. Photomicrograph of sandstone. (Lord.) 



