Concrete Matter from Atomic Origins. 409 
until the protrusion becomes unstable, and a comparatively 
small portion of the whole liquid breaks away from the main 
mass, at the thin end of the " pear. - " 
That separation must have been a sudden and violent 
catastrophe, however gradual may have been the changes of 
figure and distribution of matter which led to it. If at the 
time when it took place, the whole material was perfectly 
liquid, the act of separation would leave no permanent marks 
on either of the two bodies. After some moderate time of 
subsidence from the violent oscillations suddenly produced 
by the catastrophe, the Earth and Moon would have subsided 
into the comparatively tranquil conditions of rotating liquid 
spheroids, revolving round the centre of inertia of the two ; 
disturbed from hydrostatic equilibrium only by the inferior 
convective currents due to cooling at the surfaces ; and with 
no prospect of ever freezing into the largely unsymmetrical 
shapes which we now see on the visible half of the Moon's 
surface, and over the whole surface of the Earth. 
§ 27. To account for the evolution of present configurations 
and conditions, it seems to me that we must suppose the 
material of Moon and Earth, at the time of the separational 
catastrophe, to have reached some such condition as that 
described in § 15 : — a conglomeration of crystals with still 
liquid lava filling all the interstices between them. Such a 
conglomeration would have plasticity enough to pass through 
the changes of figure which, according to Darwin's theory, the 
material of Moon and Earth must have experienced before the 
separational catastrophe : and yet may have possessed suf- 
ficient subpermanent or permanent resistance against change 
of shape to allow them to keep permanent traces of the wounds 
left on the two bodies by the convulsive separation. 
§ 28. The scar, and subsequent surgings, left on the 
semi-plastic Earth by the tearing away of the Moon from it 
might account for persisting deviation from rotational sym- 
metry, and from equilibrium of gravity and centrifugal force, 
as great as that which is presented by the elevations of Africa, 
Asia, Europe, America, and the depths of the Atlantic, Pacific, 
and Indian Oceans. If, at the time when the Moon left the 
Earth, the material was all in the semi-solid semi-plastic con- 
dition of granite conglomerate, with a mother liquor of melted 
basalt in the interstices among the crystals, this quasi unset 
Portland cement, constituting the two bodies, might well in 
the course of fifty or one hundred million years become as 
nearly solid as we know both the Earth and Moon to be at 
present. It must however be quite understood that the 
present features of the Earth, with mountains and ravines, 
