752 
of the sea, nor is there any mention of the 
great advance in our knowledge of the 
ocean during the period of sixty-five years 
then under consideration. This omission 
may be accounted for by the fact that, at 
the time of the formation of the British As- 
sociation, knowledge concerning the ocean 
was, literally speaking, superficial. The 
study of marine phenomena had hitherto 
been almost entirely limited to the surface 
and shallow waters of the ocean, to the sur- 
vey of coasts and of oceanic routes directly 
useful for commercial purposes. Down to 
that time there had been no systematic at- 
tempts to ascertain the physical and biolog- 
ical conditions of those regions of the earth’s 
surface covered by the deeper waters of the 
ocean ; indeed, most of the apparatus neces- 
sary for such investigations had not yet 
been invented. 
The difficulties connected with the ex- 
ploration of the greater depths of the sea 
arise principally from the fact that, in the 
majority of cases, the observations are 
necessarily indirect. At the surface of the 
ocean direct observation is possible, but our 
knowledge of the conditions prevailing in 
deep water, and of all that is there taking 
place, is almost wholly dependent on the 
correct working of instruments, the action 
of which at the critical moment is hidden 
from sight. 
It was the desire to establish telegraphic 
communication between Europe and Amer- 
ica that gave the first direct impulse to the 
scientific exploration of the great ocean- 
basins, and at the present day the survey 
of new cable routes still yields each year 
a large amount of accurate knowledge re- 
garding the floor of the ocean. Immedi- 
ately before the Challenger Expedition there 
was a marked improvement in all the appa- 
ratus used in marine investigations,and thus 
during the Challenger Expedition the great 
ocean-basins were for the first time syste- 
matically and successfully explored. This 
SCIENCE. 
[N. S. Vou. X. No. 256. 
expedition, which lasted for nearly four 
years, was successful beyond the expecta- 
tions of its promoters, and opened out a 
new era in the study of oceanography. A 
great many sciences were enriched by a 
grand accumulation of new facts. Large 
collections were sent and brought home, 
and were subsequently described by spec- 
ialists belonging to almost every civilized 
nation. Since the Challenger Expedition 
there has been almost a revolution in the 
methods employed in deep-sea observations. 
The most profound abysses of the ocean are 
now being everywhere examined by sailors 
and scientific men with increasing precis- 
ion, rapidity, and success. 
The recognition of oceanography as a dis- 
tinct branch of science may be said to date 
from the commencement of the Challenger 
investigations. The fuller knowledge we 
now possess about all oceanic phenomena 
has had a great modifying influence on 
many general conceptions as to the nature 
and extent of those changes which the crust 
of the earth is now undergoing and has un- 
dergone in past geological times. Our 
knowledge of the ocean is still very incom- 
plete. So much has, however, already been 
acquired that the historian will, in all prob- 
ability, point to the oceanographical dis- 
coveries during the past forty years as the 
most important addition to the natural 
knowledge of our planet since the great 
geographical voyages associated with the 
names of Columbus, Da Gama, and Magel- 
lan, at the end of the fifteenth and the be- 
ginning 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 sci- 
ence. But, as nearly all 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 condi- 
