140 proceedings: geological society 



ical composition of the water insuring a supply of calcium salts for the 

 formation of the skeletons are essential. 



The speaker then gave a brief review of both the stratigraphic and 

 geographic distribution of Paleozoic coral reefs, calling attention to the 

 more important constituent genera. The Paleozoic coral reefs begin 

 in the lower Cambrian and extend through the Carboniferous. The 

 same groups of reef-building organisms are represented in both the Pale- 

 ozoic and Recent seas; in both they have the same facies as regards 

 growth-form; in both, their physiologic activity has resulted in the se- 

 cretion of large quantities of carbonate of lime from the surrounding 

 sea-water; and in both, submarine banks, known as coral reefs, have 

 resulted. The general similarity of the organisms and the similarity 

 in the result of their physiologic activity, suggest similarity of condi- 

 tions under which his activity took place. 



The nature of the sediments and the character of the stratification 

 of the beds in which occur the Silurian reefs of , Gotland and Cedarburg, 

 Wisconsin, and the Devonian reefs of Wisconsin and New York, were 

 reviewed. As the materials of the matrix in which the reefs are em- 

 bedded are largely fragmental, and as cross bedding and other evidence 

 of shallow water deposition is furnished, the conclusion was reached that 

 these Paleozoic reefs were formed in shallow, agitated, and presumably, 

 therefore, well-lighted, waters. 



The conditions under which Paleozoic reefs were formed were sum- 

 marized as follows: 



(a) Depth, maximum 25 fathoms; light, strong, (b) Temperature, 

 annual minimum not lower than between 60 and 70° F., and probably 

 above 70° F. (c) Water, agitated and circulating, (d) Bottom, clear 

 or relatively free from deposits of silt, (e) Composition of the oceanic 

 salts, probably the same as in the ocean of the present day. (f) Specific 

 gravity of the oceanic ivaters, probably about as in the ocean of today. 

 Certainly the specific gravity was high enough to furnish the large quan- 

 tities of calcium salts demanded by the reef organisms for the formation 

 of their skeletons. 



Bonney says in his appendix to Darwin's Structure and Distribution 

 of Coral Reefs, p. 331: "Moreover, the aporosa and madrepor aria, 

 which are now the chief reef-builders, have only become common since 

 the conclusion of Paleozoic ages, so that the largest volume of the geo- 

 logical history of the earth is excluded from consideration, because in the 

 time which it covers the habits of the reef-builders may have been dif- 

 ferent." The evidence presented by Dr. Vaughan showed in his opin- 

 ion, that the habitats of reef-building corals have always been similar. 



Sir John Murray discussed Dr. Vaughan's paper, paying especial 

 attention to the conditions under which organisms secrete large quanti- 

 ties of calcium carbonate in the ocean. He gave a brief review of the 

 distribution of the coral reefs of the globe, described the origin of coral 

 reef foundations, and outlined the theories of the formation of the var- 

 ious types of coral islands. E. S. Bastin, Secretary. 



