90 GEOLOGY. 



canic period, should have given a vast gaseous envelope, and hence 

 a history not altogether unlike that of the preceding view, though 

 less excessive in its terms. 



The modified hypothesis furnishes a better ground than the older 

 view for elucidating the volcanic activity of later periods, and for supply- 

 ing the loss of the atmosphere due to chemical combination with the 

 surface rocks; but it is not clear that it is adequate. The modifica- 

 tion is offered as a possible emendation of the more common phase 

 of the gaseo-molten hypothesis touching two radica points where 

 the latter seems to fail to meet the requirements of advancing knowl- 

 edge. 



Stages under the Modified Hypothesis. 



The stages of evolution under this view may be summarized as 

 follows : 



I. The astral eon. — The separation of the material of the earth 

 from the parent nebula and its aggregation into a rotating gaseous 

 spheroid. 



II. The molten eon. — The condensation of the rock matter of the 

 gaseous spheroid into a molten spheroid which was surrounded by a 

 hot vaporous atmosphere; but the molten spheroid nevertheless retained, 

 occluded within itself, some large part of the water of the present hydro- 

 sphere, as well as much of the carbon dioxide represented by the pres- 

 ent carbonates and carbonaceous deposits. 



III. The lithic eon. — The solidification of the molten spheroid, 

 beginning most probably at the center, on account of pressure, and 

 possibly continuing thence to the surface, but perhaps beginning also 

 at the surface, at a later stage, and solidifying downwards, the two 

 solidifying portions at length meeting, or partially meeting, giving 

 rise to essential solidity of the whole. In this respect, the theory 

 may be accommodated to the various phases of opinion on this sub- 

 ject. The first mode of solidification is not altogether favorable to 

 the modified hypothesis, for the solidification rising from below might 

 not improbably force out the larger portion of the absorbed gases 

 while the surface was yet liquid The view that the surface crusted 

 over while yet there was at least a deep molten layer below, best fits 

 the general conception, and s the main basis for the following postu- 

 late. 



