GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 329 



not have such a contact, (b) Offshore coral reefs, barriers, and 

 atolls, form on antecedent flattish basements during and after sub- 

 mergence in areas where the general ecologic conditions are suitable 

 for coral growth, as stated on page 240. This generalization applies 

 to fossil as well as to living reefs, (c) Recent rise of sea level because 

 of deglaciation has made conditions favorable for coral-reef formation 

 over enormous areas, and it is one of the important factors in causing 

 the great development of coral reefs at the present time. But in 

 some areas, as in the Fijis, the flats on which the reefs are growing 

 are coastal flats that have been brought below sea level by tilting, 

 as described by Andrews and Foye. (d) The theoretic possibility of 

 the progressive change of a fringing reef into a barrier and later into 

 an atoll, according to the Darwin-Dana hypothesis, may not be denied, 

 but no instance of such a transformation has as yet been discovered. 

 (e) The coral-reef investigation is of value to geology, not so much 

 because of what has been discovered regarding corals as it is that 

 it has led to the study of a great complex of geologic phenomena 

 among which corals and coral reefs are only incident. Further inves- 

 tigations of the phenomena associated with coral reefs are among the 

 great desiderata of geologic research. 



Suggestions as to Future Investigations. 



Before closing this discussion I will present a few suggestions that 

 to me appear pertinent. 



1. It is my belief that, although ecologic notes are of much value 

 in systematic work, not a great deal more advantage will result 

 from such ecologic investigations in areas where corals are luxuriant 

 as those conducted by Gardiner, Wood Jones, and others, including 

 myself. We need to know more of the physiology of corals, but such 

 researches must be conducted by expert physiologists. There is 

 great need for ecologic work in the waters northward and southward 

 from the coral-reef zone. Within the coral-reef zone there are three 

 faunas delimited by depth and temperature. What happens outside 

 the coral-reef zone ? Do the deeper-water forms live in shallower 

 water as the high latitudes are attained ? Is it depth or temperature 

 that causes the vertical faunal distribution within the Tropics? 

 More knowledge of the ecologic relations of the deeper-water faunas 

 in the Tropics and of the f aimas in both shoal and deep water in the 

 temperate zones of the ocean is of great importance to geologists, 

 for such knowledge would furnish a basis for interpreting the physical 

 conditions under which some of the fossil faunas lived. For some 

 years I have wished to make an investigation of the kind outlined, 

 but other duties have prevented the fulfilment of my desire. There 

 is a large amount of morphologic work needed, both on the skeletons 

 and on the soft parts of corals, but particular consideration of this 

 subject is scarcely in place here. 



