310 CONDITION OF THE FLOOR OF THE OCEAN. 



It was the desire to establish telegraphic communication between 

 Europe and America that gave the first direct impulse to the scientific 

 exploration of the great ocean basins, and at the present day the sur- 

 vey of new cable routes still yields each year a large amount of 

 accurate knowledge regarding the floor of the ocean. Immediately 

 before the Challenger expedition there was a marked improvement in 

 all the apparatus used in marine investigations, and thus during the 

 Challenger expedition the great ocean basins were for the first time 

 systematically and successfully explored. This expedition, which 

 lasted for nearly four years, was successful beyond the expectations 

 of its promoters, and opened out a new era in the study of ocean- 

 ography. A great many sciences were enriched by a grand accumu- 

 lation of new facts. Large collections were sent and brought home, 

 and were subsequently described by specialists belonging to almost 

 every civilized nation. Since the Challenger expedition there has 

 been almost a revolution in the methods employed in deep-sea observa- 

 tions. The most profound abysses of the ocean are now being every- 

 where examined by sailors and scientific men with increasing precision, 

 rapidity, and success. 



The recognition of oceanography as a distinct branch of science may 

 be said to date from the commencement of the Challenger investiga- 

 tions. The fuller knowledge we now possess about all oceanic phe- 

 nomena has ha'd a great modifying influence on many general concep- 

 tions as to the nature and extent of those changes which the crust of 

 the earth is now undergoing and has undergone in past geological 

 times. Our knowledge of the ocean is still very incomplete. So 

 much has, however, alread}^ been acquired that the historian will in 

 all probability point to the oceanographical discoveries during the 

 past forty 3 ears as the most important addition to the natural knowl- 

 edge of our planet since the great geographical voyages associated 

 with the names of Columbus, Da Gama, and Magellan, at the end of 

 the fifteenth and the beginning of the sixteenth centuries. 



It is not my intention on this occasion to attempt anything like a 

 general review of the present state of oceanographic science. But, 

 as nearly ^11 the samples of marine deposits collected during the past 

 thirty years have passed through my hands, I shall endeavor briefly 

 to point out what, in general, their detailed examination teaches with 

 respect to the present condition of the floor of the ocean, and I will 

 thereafter indicate what appears to me to be the bearing of some of 

 these results on speculations as to the evolution of the existing surface 

 features of our planet. 



DEPTH OF THE OCEAN. 



All measurements of depth, by which we ascertain the relief of that 

 part of the earth's crust covered by water, are referred to the sea sur- 



