292 EVOLTTTIONAL GEOLOGY. 



There is an hypothesis which refers it to the clashing of meteorites, 

 but in the form in which this is usually presented it does not help us 

 much. Such meteorites as have been oliserved to penetrate our atmos- 

 phere and to fall onto the surface of the earth prove on examination 

 to have had an eventful history' of their own. of which not the least 

 important chapter was a passage through a molten state; the}^ would 

 thus appear to be the products rather than the progenitors of a nebula. 

 We commence our historj', then, with a rapidly rotating molten 

 planet, not inipossibly already solidified about the center and sur- 

 rounded b}' an atmosphere of great depth, the larger part of which 

 was contributed l)v the water of our present oceans, then existing in a 

 state of gas. This atmosphere, which exerted a pressure of something 

 like 5,000 pounds to the square inch, nuist have played a very impor- 

 tant part in the evolution of our planet. The molten exterior absorbed 

 it to an extent which depended on the pressure, and which may some 

 day be learned from experiment. Under the influence of the rapid rota- 

 tion of the earth the atmosphere would be much deeper in equatorial 

 than polar regions, so that in the latter the loss of heat by radiation 

 would be in excess. This might of itself lead to convectional currents 

 in the molten ocean. The effect on the atmosphere is very difficult to 

 trace, but it is o))vious that if a high-pressure area originated over 

 some cooler region of the ocean the winds blowing out of it would 

 drive before them the cooler superficial layers of molten material, and 

 as these were replaced by hotter lava streaming from below the tend- 

 ency would be to convert the high into a low pressure area and to 

 reverse the direction of the winds. Conversely under a low-pressure 

 area the inblowing winds would drive in the cooler superficial layers 

 of molten matter that had been swept away from the anticyclones. 

 If the diflerence in pressure under the c^^clonic and anticy clonic areas 

 were considerable, some of the gas absorbed under the anticyclones 

 might escape beneath the c3x-lones, and in a later stage of cooling 

 might give rise to vast floating islands of scoria. Such islands might 

 be the flrst foreshadowings of the future continents. Whatever the 

 ultimate eft'ect of the reaction of the winds on the currents of the 

 molten ocean, it is proljable that some kind of circulation was set up 

 in the latter. The universal molten ocean was l)y no means homo- 

 geneous. It was constantl}' undergoing changes in composition as it 

 reacted chemically with the internal metallic nucleus; its currents 

 would streak the diflerent portions out in directions which in the 

 northern hemisphere would run from northeast to southwest, and thus 

 the differences which distinguish particular petrological regions of our 

 planet may have connnenced their existence at a very early stage. Is 

 it possible that as our knowledge extends we shall ])e able by a study 

 of the distribution of igneous rocks iind minerals to draw some con- 

 clusions as to the direction of these h^potlietical lava currents ? Our 



