582 NATURE 
[ Oct. 15, 1885 
However, we find that Erathosthenes, Posidonius, and other 
learned Greeks, who flourished between one and two centuries 
before our era, were in possession of ideas concerning the figure 
and position of the terrestrial globe which do not differ mate- 
rially from those of the modern geographer. They had con- 
siderable knowledge of the great wide sea, a clear perception 
of the diurnal recurrence of the tides, of their monthly cycles of 
variation, and correctly ascribed these changes to the influence 
of the moon. They speculated on the circumnavigation of the 
globe, and thus anticipated by many centuries the project of 
Columbus of sailing direct from Spain to the Indies. 
During the century immediately preceding the Christian era, 
and during the dark and middle ages, there was a large acquisi- 
tion of information with respect to the superficial extent of the 
ocean. But, when we look back on the history of knowledge 
concerning our planet, there is to be found no parallel to the 
impression produced in men’s minds and conceptions by the 
discovery of America, and the circumnavigation of the world, 
a few years later, by Magellan and Drake. The influence of 
these events and the great ideas associated with them, can be 
traced throughout the literature of the Elizabethan period ; 
Shakespeare appears to have had the mental picture of the 
great, solid, floating globe continually before him. His spirit 
seemed 
«|. . « blown with restless violence round about 
The pendant world.” 
To the great mass of people the circumnavigation of the globe 
was the practical demonstration that the earth was swung in 
space, supported alone by some unseen power ; it was the con- 
clusive proof of its globular form—a fact which must be regarded 
as the fundamental principle of all scientific geography. 
The rage for geographical exploration which set in after the 
discovery of America brought the phenomena of the ocean into 
greater prominence, but the science of the sea can hardly be 
said to have commenced till the seventeenth century, when 
Hooke and Boyle undertook their experiments as to the depth of 
the sea and the composition of ocean water; and _ several 
naturalists gave descriptions of the animals and plants inhabit- 
ing the shallow waters surrounding the land. During the 
eighteenth century there was again a large acquisition of know- 
ledge concerning the ocean, for the navigator was busy with the 
study of the winds, currents, and tides; while the two Rosses 
with other explorers and scientific men made most praiseworthy 
endeavours to investigate the greater depths of the sea during 
the first half of the present century. 
The vast abysmal regions of the great ocean basins, however, 
lay all scientifically unexplored, when about twenty years ago 
their systematic examination was undertaken by expeditions 
sent forth by our own country and by the Governments of the 
United States, Germany, Italy, France, and Norway. 
It is not easy to estimate the relative importance of the events 
of one’s own time, yet in all probability the historians of the 
reign of Victoria will point to the recent discoveries in the great 
oceans as the 1nost important events of the century with respect 
to the acquisition of natural knowledge, as among the most 
brilliant conquests of man in his struggle with nature, and 
doubtless they will be able to trace the effect of these dis- 
coveries on the literature and on the philosophic conceptions of our 
age. A mantle of mystery and ignorance has been cleared away 
from the eleven-sixteenths of the earth’s surface covered by the 
ocean, and in its place we have much definite and accurate 
knowledge of the depths of the sea. The last of the great out- 
lines showing the surface features of our globe have been boldly 
sketched ; the foundations of a more complete and scientific 
physiography of the earth’s surface have been firmly laid down. 
This evening we will endeavour to pass in review some of the 
chief phenomena of the great ocean basins, and attempt to bring 
before you some of the more important results arrived at by the 
many distinguished men who have been engaged in oceano- 
graphical researches during recent years. 
If it be remembered that the greatest depth of the ocean is 
only about five miles, and that the height of the highest mountain 
is likewise about five miles above the level of the sea, while the 
globe itself has a diameter of 8000 miles, the comparative insig- 
nificance of all the surface inequalities of the earth is at once 
forced on our attention. <A circle 66 feet in diameter having on 
its surface a depression of one inch; or a globe one foot in 
diameter, with a groove on its surface one-sixtieth of an inch in 
depth, would represent on a true scale the greatest inequality, of 
mountain height and ocean deep, on the surface of the earth. 
Misconceptions often arise, and erroneous conclusions are fre- 
quently arrived at when these proportions are not rigidly borne in 
mind. But, unimportant as these surface features may appear when 
viewed with reference to the diameter of the earth, or to the 
superficial area of an ocean several thousand miles in extent, 
still to the geologist and physical geographer the elevations and 
depressions, foldings and dislocations, vertical and lateral, which 
form these inequalities are truly gigantic, immense, profound ; 
and the more they are studied the more do they appear to be 
the result of changes taking place in a very definite and orderly 
manner in the course of the earth’s developmental history. 
Allow me to direct your attention to the maps representing 
hemispheres of the earth drawn in equal surface projection, 
The continental land of the world is coloured black, the abyss- 
mal regions are coloured red, and between these two there is a 
border or transitional area which is uncoloured. 
You will observe that the dark-coloured masses of continental 
land are, at some one point, more or less closely connected with 
similar masses ; there is usually a place where adjacent masses 
are not separated by oceans of very great depth. A traveller 
might almost journey from any one point in these regions to any 
other without once losing sight of land. If an exception must 
be made to this statement it is in the case of New Zealand and 
the Antarctic Continent, for the Chad/enger’s dredgings, which 
brought up masses of schist, gneiss, granite, sandstone, and com- 
pact limestone along the borders of the ice-barrier, show beyond 
all doubt that there is a mass of continental land at the south 
pole, but, since it is buried beneath perpetual snow, its exact 
extent is a matter of conjecture. 
The surfaces of the continents are everywhere cut into cliffand 
gorge, mountain and valley, and are continually undergoing a 
process of disintegration. Water, frost, ice, sudden changes of 
temperature, are ever tearing the solid rocks to pieces, rivers are 
transporting the fragments down to the ocean, or carrying away 
the solid earth in solution ; the bulk of this material is deposited 
in the areas bordering the continents—the uncoloured areas on 
the maps—there to form rocks which may once again become 
dry land. Sooner "or later the whole of the continents would 
in this way be reduced below the level of the waves, were not 
other forces at work producing elevation. Such forces there 
are, and they are probably more potent than the disintegrating 
and transporting forces, since there are many reasons for be- 
lieving that there is now more dry land than at any other period 
of the earth’s history. 
The continents have an average height of about goo feet 
above the level of the sea; they may be regarded as elevated 
plateaus occupying five-sixteenths of the earth’s surface. 
The abysmal regions of the earth, represented by the red colour 
on the maps, occupy eight-sixteenths, or one-half of the earth’s 
surface, and have an average depth of three miles beneath the 
surface of the waves. The greate:t depths in the Pacific are to 
the south and east of Japan, where there are abysses of over 
five miles ; and in the Atlantic the greatest depth is to the north 
of the Virgin Islands, where there is a depression of a little 
over four miles. 
From all we yet know of these abysmal areas they have not a 
diversity of peak, gorge, mountain, and valley comparable to 
those which are met with on land; they are fundamentally areas 
of deposition. It is true that the close soundings of telegraph 
engineers appear to show that in some cases there may be steep 
cliffs in the shallower depths of the ocean in volcanic areas ; yet 
the general aspect of the abysmal regions must be that of vast 
undulating plains, interrupted here and there by huge volcanic 
cones, with slopes at a very low angle. When these cones rise 
above the surface they form volcanic oceanic islands. When 
they rise nearly to the surface they are, in the tropics, often 
capped by coral atolls; but many of them are far beneath the 
waves and are covered by a white mantle of carbonate of lime— 
the dead shells and skeletons of pelagic and deep-sea organisms. 
The land of the oceanic islands is of small extent and differs 
widely in the nature of the rocks, as well as in the character of 
the terrestrial aad marine fauna and flora, from the, continents 
and continental islands. There has not been found in the 
abysmal areas any land made up of gneisses, schists, sandstones, 
or compact limestones ; nor have fragments of these sedimentary 
formations been found in the erupted rocks of the volcanic 
islands, though they are frequent in the volcanic eruptions on 
the continental areas. 
We may, indeed, compare the oceanic islands to the fresh and 
salt water lakes scattered over the surface of the continents and 
