O2 Joty—An Hstimate of the Geological Age of the Earth. 
dense vapour, or sinking into hotter layers beneath immediately resumed its 
vapourous state. Its condition was, in fact, highly unstable as regards upward or 
downward motion ;* finally the temperature sank till water established itself upon 
the surface: here and there over hotter areas doubtless flashing into vapour, but 
gradually gaining a resting-place upon the surface.t For along period the fall in 
pressure attending its own condensation must have maintained it in a state of 
ebullition. 
Effects were produced at this stage which may well claim here a moment’s 
consideration. 
Sensible shrinkage due to secular cooling, and the great earth-folding which 
has since wrinkled the Earth’s surface had not yet taken place. Let us suppose a 
depression anywhere upon the comparatively uniform surface receiving the 
precipitated water. Over this area the pressure is increased, elsewhere it is 
reduced. The effect oi this is to cause, on the one hand, a further depression of 
the early sea bottom, and to establish a drainage into it, and on the other to 
facilitate the expansion and extrusion of any heated volatile matter held in solution 
in the lavas beneath the dry land; a diminution of density of the land masses and 
corresponding upheaval. Further precipitation of water would widen and deepen 
the early oceans. Finally the uniform pressure of about 300 atmospheres becomes 
concentrated asa pressure of some 400 atmospheres over perhaps 38; of the Earth’s 
area, if we assume some such concentration of water as at present exists. The 
several conditions attending the gradual precipitation of the gaseous envelope 
upon the surface render it improbable that a uniform ocean covering the entire 
globe ever existed, even if it cow/d have remained in equilibrium on a thinly crusted 
Earth possessing an energetic substratum. 
The effects of this new distribution of pressure must have been to flood the 
land areas with lavas extruded from beneath. A change of pressure of from 3800 
atmospheres to one comparatively nil might be represented by an unloading of our 
present continental areas to the extent of 3600 feet of rock of a specific gravity of 
2°5.t And this unloading must have been effected in a comparatively short 
period—“‘ instantaneously,” if contrasted with the slow unloading effected by 
denudation.§ Such a redistribution of pressures must have inaugurated remarkable 
* ( A Theory of Sunspots.” By J. Joly. Roy. Dub. Soc. Proc., N.S. Vol. vur., 1898, pp. 697-700. 
+ Professor Sollas, F.R.S., in his lectures in dwelling on the facts of the inception of ocean basins, 
has frequently pointed out that these must have dated from the rainfall attendant on the fall of tempera- 
ture to the critical temperature of water. 
+ One effect of this would be that over the land surfaces the melting point of a rock such as Diabase 
would be raised about 8° C. This would tend to confer some greater rigidity on the exposed crust of the earth. 
§ It is not to be supposed that tidal disturbances permitted this allocation of the surface to take place 
quietly, and without swaying at each vibration of our satellite, then possibly much closer to the terrestrial 
surface. 
