GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 331 



5. Shore-line history is obviously an essential part of the study of 

 coral reefs. But the entire story can not be deduced from the infor- 

 mation furnished by all of the lines of investigation above suggested. 

 The configuration of the sea bottom needs to be studied, both in 

 plan and profile. Notwithstanding the gr^at amount of work that 

 has been done on oceanic hydrography, close attention to the minor 

 configuration of the sea bottom and attempts to draw inferences from 

 such studies are of very recent date. Since most hydrographic 

 charts were not intended to serve as a basis for such researches, we 

 are fortunate that we can extract so much information from them. 

 Although it is probable that a much larger amount of data is on 

 the charts than has as yet been utilized, that additional hydrographic 

 research is needed is obvious. What are submarine slopes off the 

 divide ends in reef-encircled islands? What is the character of the 

 slopes off both the reefs and the breaks in the reefs ? The problem 

 of submerged terraces, flats and fronts, has barely been touched. 

 How extensively are such features present, and what is their signifi- 

 cance ? These considerations lead to inquiries regarding wave base, 

 the rate of motion of the water, the erosional and transporting power 

 of the water while in motion at different rates, and the relations of 

 erosion and transportation to depth. Although the factors men- 

 tioned are among those that determine the profile of subaqueous 

 equilibrium and must be considered in their relation to it, there are 

 other factors, among which are the initial slope of the bottom, the 

 hardness and degree of consolidation of the material forming the 

 bottom, and the attitude, height, and hardness of the rocks at the 

 shore. More information on this complex of problems is urgently 

 needed. 



Sea level rises or falls with reference to the land, or the land rises 

 or falls with reference to the sea level. That there have been many 

 shifts in the position of the strand line since the beginning of Pleisto- 

 cene time is known to every geologist. He also knows that in many 

 areas shifts have been caused by tilting or flexing of parts of the 

 earth's crust, and that there must have been lowering of sea level 

 while there were great continental ice sheets, followed by rise of 

 sea level when the ice sheets melted. How much of the geologically 

 Recent change in the position of strand line is to be attributed to 

 climatic causes and how much to differential crustal movement? 

 More accurate and areally more extensive studies of shore-line his- 

 tory should enable a more precise evaluation of the effects due to 

 each than is now possible. Such investigations must not be confined 

 to tropical and subtropical areas — they must be world wide. 



Then there is the problem of Pleistocene wave cutting. I believe, 

 for reasons stated elsewhere, that Daly has overevaluated the effects 

 of Pleistoceme marine planation. Has either of us really enough 



