CHAPTER X. 



MORPHOLOGY AND LITHOGENESIS OF THE TRUE ORGANIC 

 OR BIOGENIC ROCKS. ZOOGENIC DEPOSITS. 



Biogenic rocks, or Bioliths as Chr. G. Ehrenberg has termed 

 them, are deposits of organic material, or material formed through 

 the physiological activities of the organisms. In general, Bioliths 

 may be divided into those in which the organic matter is preserved 

 in the form of carbon or compounds of carbon, and those in which 

 only the inorganic mineral matter, abstracted from the food or 

 the medium in which the organism lives (air, water, or soil), is 

 preserved. The former are almost wholly restricted to plant- 

 formed (phytogenic) deposits, or phytoliths, and the latter are 

 best represented by animal-formed (zoogenic) deposits or zooliths. 

 As the organic carbon deposits, whether plant or animal, all have 

 the property of combustibility, they have been designated causto- 

 biolitJis/'' while the non-combustible organic deposits of purely min- 

 eral character are designated acaustobioUths. 



The following classification of the types of biogenic deposits, 

 or Bioliths (Biolites), may be made: 



A. Zoogenic Deposits or Zooliths. 



1. Coral reefs. 



2. Sponge reefs. 



3. Bryozoa reefs. 



4. Shell colonies. 



5. Shell limestones. 



6. Crinoidal limestones. 



7. Calcareous oozes. 



a. Foraminiferal oozes. 



b. Pteropod oozes. 



c. Cyprid oozes. 



*From Kav(rTiK6s = capable of burning, Bios, life, \l9os, stone. Caustoliths of 

 inorganic origin also exist: e. g., sulphur deposits. 



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