8 The American Geologist. January, 1905 
as sufficient for the development of geological phenomena. 
Yet the subject can not be regarded as settled until our 
knowledge of conductivities is more complete. An iron nu- 
cleus, for example, would imply greater conductivity of the 
interior and a higher age for the earth than that computed 
by King, though probably well within the range explicitly 
allowed by lord Kelvin in view of the uncertainty of this 
datum. 
The researches of Kelvin and Darwin, supplementing 
those of Kant and others, have left no doubt that the moon 
was formerly closer to the earth than it now is, and that the 
rotation of the latter was more rapid, involving a greater 
ellipticity of the meridan than it now shows. In a fluid or 
Cartesian earth the change of figure might have produced 
little effect on the structure of the planet. If the earth is 
chiefly a mass of crystalline nickel steel, it is very possible 
that such a change in the figure of equilibrium might rupture 
it. Since the epoch at which the earth rotated in 5 hours 
30 monutes the polar axis must have elongated by several 
per cent., most of it before the time of rotation was reduced 
to II hours.* Were the earth chiefly composed of forged 
steel, such elongation might be produced by plastic deform- 
ation ; but meteoric iron is rather comparable with cast iron, 
or better still, with relatively brittle, unforged cement steel, 
and might break. 
Now it is an indubitable fact that a majority of the out- 
lines of the great oceanic basins and the chief tectonic lines 
of the globe, lie nearly on great circles tangent to the Arctic 
ocean and to the Antarctic continent.t These lines, or most 
of them, are of extremely high geological age, their main 
features having found expression as early as the oldest 
known fossils and in some cases still earlier. It appears to 
•Compare Thompson and Tait, 'Nat. Phil.,' Sec. 772, where the 
rotational period and eccentricity are given for a fluid of the mass of 
the earth and possessing its mean density. When the period is 5h. 
30m., this table grives the data for computing that the polar axis has 
a length equal to 0.95 of the length which it has when the period is a 
sidereal day. For rotation in lOh. 57m. the polar axis is 0.99 times that 
for a day. 
t In 1857 professor R. Owen, of Tennessee, and independently, Ben- 
jamin Pierce, called attention to the tangency of the coast lines to the 
polar circles (not to the coast lines of the arctic sea and tlie antarctic 
continent), each attributing the facts to the influence of the sun. In 
the first 'Yearbook' of the Carnegie Institution I failed to refer to 
these publications. 
