BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 14, pp. 337-352, PLS. 47-48 SEPTEMBER 2, 1903 



PALEOZOIC CORAL REEFS 



BY AMADEUS W. GRAB A U 



[Read before the Society December 30, 1902) 



CONTENTS 



Page 



Introduction 337 



Description of coral reefs 338 



Hamilton reefs of Alpena, Michigan 338 



Reefs of the Traverse Bay region 339 



Onondaga reef of Williamsville, New York 340 



Siluric reefs of southeastern Wisconsin 341 



Siluric coral reefs of Gotland 343 



Devonic and Carbonic reefs of Belgium 344 



Summary of characters of Paleozoic coral reefs 344 



Comparison with modern coral reefs 345 



Origin of the coral sand 346 



Bryozoa reefs 348 



Classification of reef limestones 348 



Genesis of the limestones 348 



Calcirudite 349 



Calcarenite 349 



Calcilutite 350 



Suggested classification of limestones 351 



Il^TRODUCTION 



During the prosecution of field work in the Hamilton limestones of 

 Michigan, I became aware of the existence of well marked isolated coral 

 mounds or hillocks in the otherwise stratified and almost unfossiliferous 

 limestones. These coral hillocks are particularly well exposed in the 

 vicinity of Alpena, where several quarries have been opened in them. 

 In his survey of the region Rominger spoke of them as " bubble-like " 

 upheavals of the strata. Recent favorable sections in the quarries per- 

 mitted the study of these hillocks in detail, when their reef character 

 became apparent. A brief account of the reefs was published in the 

 American Geologist, September,* and a more extended one, with a cross- 

 section, in the annual report of the Geological Survey of Michigan for 



*Yol. xxviii, 1901, p. 182. 

 XLVIII— Bull. Geol. Soc. Am., Vol. 14, 1902 (337) 



