CORAL REEFS 385 



8. Siliceous oozes. 



a. Racliolarian oozes. 



b. Sponge spicule oozes. 



9. Phosphate (guano) deposits. 

 B. Pliytogcnic Deposits or PhytolitJis. 



1. Nullipore reefs and limestones, 



2. Algous travertine. 



3. Phytogenic oolites. 



4. Chara marls and limestones. 



5. Diatomaceous oozes. 



6. Caustophytoliths. 



a. Sapropeliths. 



b. Peat. 



c. Lignites, brown coal, etc. 



d. Coals. 



e. Deep sea vegetal deposits. 



In the present chapter only the zoogenic deposits will be dis- 

 cussed, the phytogenic being referred to the next chapter. 



CORAL AND OTHER REEFS. 



Coral reefs have been formed in all geological periods, from the 

 Cambric to the present, and recent investigations seem to indicate 

 the existence of archseocyathid corals in reef-like association during 

 the pre-Cambric (Animikie) in the Canadian region. Reefs are 

 complex structures, and corals often play only a minor part in their 

 construction. Calcareous alg?e, or Nullipores, are commonly among 

 the most important reef organisms (Marshall Howe-50), while 

 Hydrocorallines are equally abundant. In fossil reefs Sponges and 

 Bryozoa are often the most important reef organisms. The term 

 coral will be used here in its more general or comprehensive sense, 

 so as to include the hydrocorallines, both the recent millepores and 

 their fossil representatives, the Stromatoporoids. Among the corals 

 proper two classes are represented : Madrcporaria, or stone corals, 

 and the Alcyonaria. The latter, however, furnish only a small con- 

 tribution to the reef. Many other lime-secreting organisms occur 

 besides corals and nullipores. They are, however, of secondary 

 significance, and, on the whole, contribute only a fraction of its 

 mineral matter to the reef. 



The general characteristics of modern coral reefs will first be 

 discussed, and this will be followed by a review of reefs of the past. 



