continental slope in question is of first importance. Still aore is 

 this essential as a basis for weighing the validity of the ass"amed 

 shifts in sea level that are integral in the glacial- control theory 

 of coral reef formation. The relation to the coral reef problems of 

 submarine volcanoes is equally evident. Pendul^on measurements of the 

 gravity, for some distance out at sea, are also needed to combine 

 with the _ geologic data above sea level as evidence whether the region 

 in question be one of recent subsidence, of emergence, or stationary; 

 i.e., as a test of the crustal stability of the coral reef regions, 

 especially of the TTest-Tropical Pacific. 



This matter of depth, and of the local variations in crustal 

 stability, is of great interest to the palaeontologist, and to the 

 zoogeographer, as well as to the dynainic geologist, for its bearing 

 on possible former land connections which have been postulated to 

 explain the distribution of terrestrial animals and plants, as at 

 present existing; equally to account for the continental separations 

 by wnich the different floral and faunal areas (once continuous) are 

 now isolated from one another. Changes in the depths of epicontinent- 

 al seas, and in the degree to which the great oceans have been in 

 free corjuuni cation with one another in the ^ast, equally concern the 

 marine biologist as factors controlling the* dispersal routes of many 

 marine organisms, and as affecting the ocean currents that transport 

 animal and plant species. 



The changes in the ocean currents that must necessarilv follow 

 any considerable alteration in the level of the sea floor, or in the 

 shapes of the land masses, also concern the meteorologist, because 

 of _ their influence on the evolution of climates. Of interest in 

 tnis connection is the question what confi^ration of the old northern 

 oceans was reflected by the mild climate of the polar regions in 

 Socene-IIiocene times; a mildness made evident by the discovery in the 

 Arctic of fossil remains of animals and plants belonging to groups 

 tnat can now only live much farther south. 



Until very recently so^onding in deep water (carried on with wire) 

 onnn^ laborious and time-consuming process; to take a soundin-'^ in 

 2000 fathoms, for instance, required at least an hour after the ship 

 had been stopped. From this it has naturally followed that our 

 present knowledge of the sha-oe of the sea floor is inversely pro- 

 portional to the depth of the water, and to the distance from land; 

 the less frequented, too, any part of the sea, the less we know about 

 its depth, 



Faturally, information is most extensive for shoal waters near 

 land. In fact, as pointed out elsewhere (Page 84 ), our charts of 

 tne more frequented coasts leave little to be desired from the 

 navigator's standpoint. But the various investigators who have 

 attempted geologic interpretation of the configuration of the sea 

 bottom, especially near land, have constantly faced the obstacle 

 that perhaps no existing charts of the American coast line are whollv 

 satisfactory, except for one covering a limited area off California 

 prepared within the past year through the cooperative effort of the 

 uoast and Geodetic Survey and of the Scripps Institution, The same, 

 Uith local exceptions) is also true for European waters, while the 



