248 CONFERENCE OlS PALEOZOIC PALEOGEOGRAPHY 



turned, but most of them appear to lie in their normal position of growth. In 

 tome places the crystalline coral sand forms most of the reef exposed, the 

 large coral heads being scattered through the sand. The sand shows no 

 stratification, so far as observed. The sand filling the cavities of the reef is 

 generally much coarser than that forming the normal sediments on its flanks. 

 In places at some distance from the center of the reef the rock consists of a 

 breccia made up of brachiopods, bryozoa, and the small branching corals, with 

 a plentiful interspersing of the joints of crinoid stems." 



Concerning the reefs of the Traverse Bay region of Wisconsin^ Grabau 

 says: 



"At intervals the section passes near enough to the reef to show the pres- 

 e i( e of numerous coral fragments. The fragments are all much worn and 

 broken, and are embedded as boulders or pebbles in the stratified lime sands. 

 Where they are abundant they constitute a veritable coral conglomerate 

 (calcirudite) , such as may be found near the borders of modern reefs. Good 

 exposures of such conglomeratic beds are found in the quarries and shore 

 sections east of Petoskey, where these coral pebbles (chiefly Acervularia and 

 Favosltes and the hydrocoralline Stromatopora) give the rock a strikingly 

 mottled appearance. Not infrequently seams of carbonaceous material sepa- 

 rate some of the layers of limestone, and in these plant remains are not un- 

 common. Within the thicker beds themselves the phenomena of contem- 

 poraneous erosion, of the wedging out of strata, and, occasionally, of cross- 

 bedding and ripple marks, are met with. Indeed, all the phenomena seen in 

 heavy bedded sandstones are found in these fragmental deposits." 



He says, in describing the Onondaga reef of Williamsville, New 

 York: 



"The corals of the bedded limestone in the neighborhood of the reef are 

 fragmental and may lie in almost any position. They indicate considerable 

 wave activity around the margins of the reef." 



By applying the criteria derived from the study of the conditions 

 under which Coelenterates may live and secrete calcium carbonate, and 

 from the investigation of the physical characters, the bedding, and strati- 

 fication of the sediments in which the coral reefs are embedded, the 

 conclusions seem to follow: 



DEPTH OF WATER AND INTENSITY OF LIGHT 



An examination of the modern reef-forming corals has shown that 

 they are effective workers only in depths less than 25 fathoms. Because 

 of the zoologic affinity of the organisms, their similarity in growth-form, 

 and the similarity of the result of their physiological activity, the con- 

 clusion appears justified that the reef -forming Coelenterates of Paleozoic 

 time lived in a depth of water similar to that in which those of Eecent 

 time live, or the Paleozoic reefs were formed in water not over 25 fathoms 

 in depth. 



