352 A. W. GRABAU — PALEOZOIC CORAL REEFS 



{e) Crinoidal limestones, composed chiefly of the stem 

 joints of crinoids which become dissociated on the 

 death of the animal. 



(/) Oolites and other stratified deposits due to lime-secret- 

 ing algge which are not attached. Here belongs the 

 oolite of Great Salt lake. 



II. Under the clastic limestones we have, as already noted : 



C. Calcirudite, comprising coarsely fragmental or "rudaceous" rocks 



derived : 



(5) From contemporaneous organic limestones, including : 



{g) Coral breccia. 



(/i) Coral conglomerate. 



(i) Shell breccia. 



( j) Shell conglomerate, or 



(6) From older limestones, including : 



{k) Limestone breccia. 



(1) Limestone conglomerate. 



D. Calcarenite, comprising moderately fine or " arenaceous " rocks, derived : 



(7) From contemporaneous organic limestones, including: 



{m) Coral and shell-sand rock, aqueous, generally marine, 



and 

 (n) Ji^olian coral and shell sand rock. 



(8) From older limestones, comprising: 



(o) Limestone sand rock, probably indistinguishable from 

 (m), but recognizable by the absence or scarcity of 

 organic remains in the formation in which it occurs. 



E. Calcilutite, comprising fine grained, compact, or "lutaceous" rocks, 



formed of rock flour, generally with conchoidal fracture, and derived : 



(9) From contemporaneous organic limestones ground into flour, 



comprising : 



(p) Lime-flour rocks, from coral reefs, shell heaps, etcetera, 

 and 

 (10) From older limestones, comprising : 



iq) Lime-mud rocks, generally well stratified and including 

 pure carbonate rocks and water limes in which there 

 is an argillaceous admixture. 



Through metamorphism all the above rocks will be changed to marble. 



The classification here given is intended merely as a suggestion. I 

 believe that the genetic method will eventuall}^ be followed in the classi- 

 fication of sedimentary rocks, as Walther has so strongly advocated. 



With refinement in classification it will probably be necessary to cre- 

 ate many new distinctive terms of limited meaning, so that the old time- 

 honored names of limestones, sandstones, slates, shales, etcetera, will be 

 used only in more general discussions. 



