PHYSIOGRAPHIC PROBLEMS OF TODAY 529 



circumstances endeavors to follow many of the paths he finds leading 

 into the unknown, is replaced to a large extent by well-organized and 

 well-equipped scientific expeditions. It is to such systematically 

 planned campaigns, in which the physiographer and representatives 

 of other sciences mutually aid each other, that the greatest additions 

 to man's knowledge of the earth's surface are to be expected. The 

 most extensive of the unexplored or but little-known portions of the 

 surface of the lithosphere, in which a rich harvest awaits the properly 

 equipped expedition, are the sea-floor and the north and south polar 

 regions. As is well known, splendid advances have been made in 

 each of these fields, but, as seems evident, much more remains to be 

 accomphshed. 



In the branch of physiography appropriately termed "oceanog- 

 raphy" the problems in view are the contour of the sea-floor, or its 

 mountains and deeps, plains and plateaus, the manner in which each 

 inequahty of surface came into existence, and the various ways it is 

 being modified. In both of these directions the interests of the 

 physiographer merge with those of the biologist and the geologist. 

 One phase of the study of the ocean's floor which demands recognition 

 is that the topographic forms there present are such as have been 

 produced almost entirely by constructional and diastrophic agencies, 

 free from complications due to erosion which so frequently obscure 

 the result of hke agencies on the land. For an answer to the question : 

 What would have been the topography of land areas, had there been 

 no subaerial decay and denudation ? the topography of submarine 

 regions furnishes at least a partial answer. The sounding line in the 

 Caribbean region has furnished examples of topography due, as it 

 seems, mainly to differential movements of blocks of the earth's crust 

 bounded by faults, which have not been modified by subaerial denuda- 

 tion. In a similar way, as is to be expected, a survey of other portions 

 of the at present water-covered surface of the hthosphere will supple- 

 ment our knowledge of the emerged portions of the same rock-envelope, 

 and assist in an important way in the deciphering of their histories. 



In the Arctic and Antarctic regions, where all is unknown, systematic 

 research may be expected not only to extend many branches of physio- 

 graphic study, but to bring to the front as yet unsuspected problems. 



The larger of the unexplored regions of the earth, however, are not 



