SEPTEMBER 28, 1899] 
food to be picked up, and at other times as a lure or a warning. 
All these peculiar adaptations indicate that the struggle for life 
may be not much less severe in the deep sea than in the shallower 
waters of the ocean. 
Many deep-sea animals present archaic characters ; still the 
deep sea cannot be said to contain more remnants of faunas 
which flourished in remote geological periods than the shallow 
and fresh waters of the continents. Indeed, king-crabs, 
Lingulas, Trigonias, Port Jackson sharks, Cevatodus, Lepido- 
siren, and Protofterus, probably represent older faunas than 
anything to be found in the deep sea 
Sir Wyville Thomson was of opinion that, from the Silurian 
period to the present day, there had been as now a continuous 
deep ocean with a bottom temperature oscillating about the 
freezing point of fresh water, and that there had always been an 
abyssal fauna. I incline to the view that in Paleozoic times the 
ocean-basins were not so deep as they are now; that the ocean 
then had throughout a nearly uniform high temperature, and 
that life was either absent or represented only by bacteria and 
other low forms in great depths, as is now the case in the Black 
Sea, where life is practically absent beyond roo fathoms, and 
where the deeper waters are saturated with sulphuretted 
‘hydrogen. This is not, however, the place to enter on specu- 
lations concerning the origin of the deep-sea fauna, nor to 
dwell on what has been called ‘‘ bipolarity”’ in the distribution 
of marine organisms. 
Evolution of the Continental and Oceantc Areas. 
I have now pointed out what appears to me to be some of 
the more general results arrived at in recent years regarding the 
present condition of the floor of the ocean. I may now be 
permitted to indicate the possible bearing of these results on 
opinions as to the origin of some fundamental geographical 
phenomena ; for instance, on the evolution of the protruding 
continents and sunken ocean-basins. In dealing with such a 
problem much that is hypothetical must necessarily be intro- 
duced, but these speculations are based on ascertained scientific 
facts. 
The well-known American geologist, Dutton, says: ‘‘It has 
been much the habit of geologists to attempt to explain the pro- 
gressive elevation of plateaus and mountain platforms, and also 
the folding of strata, by one and the same process. I hold the 
two processes to be distinct, and having no necessary relation to 
each other. There are plicated regions which are little or not 
at all elevated, and there are elevated regions which are not 
plicated.” Speaking of great regional uplifts, he says further : 
** What the real nature of the uplifting force may be is, to my 
mind, an entire mystery, but I think we may discern at least 
one of its attributes, and that it is a gradual expansion or a 
diminution of density of the subterranean magmas. . .. We 
know of no cause which could either add to the mass or diminish 
the density, yet one of the two must surely have happened. . . . 
Hence I infer that the cause which elevates the land involves an 
expansion of the underlying magmas, and the cause which 
depresses it is a shrinkage of the magmas ; the nature of the 
process is at present a complete mystery.” I shall endeavour to 
show how the detailed study of marine deposits may help to 
solve the mystery here referred to by Dutton. 
The surface of the globe has not always been as we now see 
it. When, in the past, the surface had a temperature of about 
400° F., what is now the water of the ocean must have existed 
as water vapour in the atmosphere, which would thereby—as 
well as because of the presence of other substances—be increased 
in density and volume. Life, as we know it, could not then 
exist. Again, science foresees a time when low temperatures, 
like those produced by Prof. Dewar at the Royal Institution, 
will prevail over the face of the earth. The hydrosphere and 
atmosphere will then have disappeared within the rocky crust, 
or the waters of the ocean will have become solid rock, and 
over their surface will roll an ocean of liquid air about forty feet in 
depth. Life, as we know it, unless it undergoes suitable secular 
modifications, will be extinct. Somewhere between these two 
indefinite points of time in the evolution of our planet it is our 
privilege to live, to investigate, and to speculate concerning the 
antecedent and future conditions of things. 
When we regard our globe with the mind’s eye, it appears 
at the present time to be formed of concentric spheres, very 
like, and still very unlike, the successive coats of an onion. 
Within is situated the vast nucleus or cextrosphere ; surrounding 
this is what may be called the ¢e/osphere (tnxTds, molten), a 
NO. 1561, VOL. 60] 
NATURE 
525) 
shell of materials in a state bordering on fusion, upon which 
rests and creeps the /zthosphere. Then follow hydrosphere and 
atmosphere, with the included dzosphere (Bios, life). To the 
interaction of these six geospheres, through energy derived 
from internal and external sources, may be referred all the 
existing superficial phenomena of the planet. 
The vast interior of the planetary mass, although not under 
direct observation, is known, from the results of the astronomer 
and physicist, to have a mean density of 5°6, or twice that of 
ordinary surface rock. The substances brought within the 
reach of observation in veinstones, in lavas, and hypogene 
rocks—by the action of water as a solvent and sublimant— 
warrant the belief that the centrosphere is largely made up of 
metals and metalloids with imprisoned gases. It is admitted 
that the vast nucleus has a very high temperature, but so enor- 
mous is the pressure of the superincumbent crust that the 
melting point of the substances in the interior is believed to be 
raised to a higher value than the temperature there existing— 
the centrosphere in consequence remains solid, for it may be 
assumed that the melting point of rock-forming materials is 
raised by increase of pressure. Astronomers, from a study of 
precession and nutation, have long been convinced that the 
centrosphere must be practically solid. 
Recent seismological observations indicate the transmission 
of two types of waves through the earth—the condensational- 
rarefactional and the purely distortional—and the study of these 
tremors supports the view that the centrosphere is not only 
solid, but possesses great uniformity of structure. The seis- 
mological investigations of Profs. Milne anid Knott point also 
to a fairly abrupt boundary or transition surface, where the solid 
nucleus passes into the somewhat plastic magma on which the 
firm upper crust rests. 
In this plastic layer or shell—named the ¢ehtosphere—the 
materials are most probably in a state of unstable equilibrium 
and bordering on fusion. Here the loose-textured solids of the 
external crust are converted into the denser solids of the nucleus 
or into molten masses, at a critical point of temperature and 
pressure; deep-seated rocks may in consequence escape 
through fissures in the lithosphere. Within the lithosphere 
itself, the temperature falls off so rapidly towards the surface as 
to be everywhere below the melting point of any substance 
there under its particular pressure. 
Now, as the solid centrosphere slowly contracted from loss of 
heat, the primitive lithosphere, in accommodating itself— 
through changes in the tektosphere—to the shrinking nucleus, 
would be buckled, warped, and thrown into ridges. That these 
movements are still going on is shown by the fact that the 
lithosphere is everywhere and at all times in a slight but 
measurable state of pulsation. The rigidity of the primitive 
rocky crust would spermit of considerable deformations of the 
kind here indicated. Indeed, the compression of mountain 
chains has most probably been brought about in this manner, 
but the same cannot be said of the elevation of plateaus, of 
mountain platforms, and of continents. 
From many lines of investigation it is concluded, as we have 
seen, that the centrosphere is homogeneous in structure. Direct 
observation, on the other hand, shows that the lithosphere is 
heterogeneous in composition. How has this heterogeneity 
been brought about? The original crust was almost certainly 
composed of complex and stable silicates, all the silicon dioxide 
being in combination with bases. Lord Kelvin has pointed out 
that, when the solid crust began to form, it would rapidly cool 
over its whole surface; the precipitation of water would 
accelerate this process, and there would soon be an approxim- 
ation to present conditions. As time went on the plastic or 
critical layer—the tektosphere—immediately beneath the crust 
would gradually sink deeper and deeper, while ruptures and re- 
adjustments would become less and less frequent than in earlier 
stages. With the first fall of rain the silicates of the crust 
would be attacked by water and carbon dioxide, which can at 
low temperatures displace silicon dioxide from its combinations. 
The silicates, in consequence, have been continuously robbed of 
a part, or the whole of their bases. The silica thus set free 
goes ultimately to form quartz veins and quartz sand on or 
about the emerged land, while the bases leached out of the 
disintegrating rocks are carried out into the ocean and ocean- 
basins. A continuous disintegration and differentiation of 
materials of the lithosphere, accompanied by a sort of migration 
and selection among mineral substances, is thus always in pro- 
gress. Through the agency of life, carbonate of lime accumulates 
