
F. Sect. II.] CHANGES OF EARTH’S CENTRE OF GRAVITY. 19 
total displacement of 285 feet, thus producing a rise of level at the 
north pole of 285 feet, and in the latitude of Edinburgh of 234 feet.” 
_ A very considerable additional displacement would arise from the 
increment of water to the mass of the ocean by the melting of the 
ice. Supposing half of the two miles of Antarctic ice to be replaced 
_ by an ice-cap of similar extent and one mile thick in the northern 
hemisphere, the other half bemg melted into water and increasing 
the mass of the ocean, Dr. Croll estimates that from this source an 
extra 200 feet of rise would take place in the general ocean level, 
so that there would be a rise of 485 feet at the north pole, and 434 
feet in the latitude of Kdinburgh.* An intermittent submergence 
and emergence of the low polar lands might thus be due to the 
alternate shifting of the centre of gravity. 
To what extent this cause has actually come into operation in 
past time cannot at present be determined. It has been suggested 
that the “raised beaches” or old sea-terraces, so numerous at 
various heights in the north-west of Europe, might be due to the 
transference of the oceanic waters and not to any subterranean 
movement, as generally believed. But if such had been their origin, 
they ought to have shown evidence of a gradual and uniform decline 
in eleyation from north to south. No such feature, however, has 
been detected. On the contrary, the levels of the terraces vary 
_ within comparatively short distances. Though numerous on both 
sides of Scotland, they disappear among the Orkney and Shetland 
islands, although these localities were admirably adapted for their 
formation and preservation.” T’he conclusion must be drawn that 
the “raised beaches” cannot be adduced as evidence of changes of 
the earth’s centre of gravity, but are due to local and irregular 
subterranean movement. (See Book III. Part I. Section iii. § 1.) 
§ 7. Results of the Attractive Influence of Sun and Moon on 
_ the Geological Condition of the Earth.—Many speculations have 
been offered to account for supposed former greater intensity of geo- 
_ logical activity on the surface of the globe. T'wo causes for such greater 
intensity may be adduced. In the first place, if the earth has 
cooled down from an original molten condition, it has lost, in cool- 
ing, a vast amount of potential geological energy. It does not 
necessarily follow, however, that the geological phenomena resulting 
_ from internal temperature have, during the time recorded in the 
accessible part of the earth’s crust, been steadily decreasing in 
magnitude. We might, on the contrary, contend that the increased 
resistance of a thickening cooled crust may rather have hitherto 
intensified the manifestations of subterranean activity by augmenting 
the resistance to be overcome. In the second place, the earth may 
have been more powerfully affected by external causes, such as the 
greater heat of the sun, and the greater proximity of the moon. 
1 Croll, Geol. Mag., new series, i. (1874), p. 347; Climate and Time, chaps. xxiii. 
and xxiv. 
2 Nature, xvi. (1877) p. 415. 
3 C2 
