250 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



The intensity of the light on the Paleozoic reefs is a corollary of the 

 depth. Sunlight can penetrate beyond 25 fathoms in depth; therefore 

 the Paleozoic reef corals lived within the region of strong light ; and the 

 opinion is ventured that the intensity of the light was a controlling fac- 

 tor in limiting the distribution of these organisms in Paleozoic time, as 

 it is at present. 



TEMPERATURE 



In summarizing the data on the conditions in which modem reefs 

 are formed^ it was stated that the annual minimum temperature must 

 not be below QS degrees Fahrenheit and that the annual mean tempera- 

 ture must be above 70 degrees Fahrenheit. In the quotation given from 

 Sir John Murray on the influence of temperature on the secretion of 

 calcium carbonate by marine organisms is the statement: 



"It thus appears that the most favorable conditions for lime-secreting organ- 

 isms are met with in the warm, equable tropical waters of the ocean, and 

 here, as a matter of fact, we find the greatest development of corals and the 

 largest number of lime-secreting pelagic organisms. In the polar areas and 

 in the cold water of the deep sea there is, as is well known, a feeble develop- 

 ment of all carbonate of lime structures in marine organisms." 



A high temperature is necessary for vigorous organic metabolism and 

 facilitates the secretion of carbonate of lime. The size of some of the 

 Paleozoic coral heads indicates how vigorous was this secretion by the 

 Paleozoic zoophytes. From an examination of modern reefs and a study 

 of the conditions favorable for the organic secretion of large masses of 

 the carbonate of lime, the deduction seems safe that the Paleozoic coral 

 reefs were formed in water of rather high temperature, the annual mini- 

 mum not being lower than a temperature between 60 and 70 degrees 

 Fahrenheit ; and the annual mean, probably above 70 degrees Fahrenheit. 



MOVEMENT OF OCEANIC WATERS 



That the waters surrounding the Paleozoic reefs were in motion, not 

 stagnant, needs only brief discussion. That the waters were agitated is 

 indicated by the coarseness of the sediments on some of the reefs and by 

 such phenomena as ripple-marking. 



CHARACTER OF THE BOTTOM 



For modern reefs a comparatively clean and rather firm bottom is nec- 

 essary for the growth of zoophytes. The organisms need proper basal 

 support, and the accumulation of fine sediment is fatal to them. We 

 may be confident that similar conditions were necessary in Paleozoic time. 



COMPOSITION OF THE OCEANIC SALTS 



An opinion on the composition of the oceanic salts in the Paleozoic 

 era can not be based on any very definite evidence, but there seems no 



