446 L, Scemann oti the Unity of Geological 



of the earth,) would lead us to suppose the existence there of a 

 peculiar condition of things ; science has, however, as yet no 

 means of appreciating the action of a heat so excessive as that 

 which is required to maintain the alkaline metals in a gaseous 

 state, and it appears possible that if the temperature of the sun 

 were reduced to that of the earth its density would also be ap- 

 proximated to that of our planet. However this may be, the 

 analogies of Leverrier's theory with the observations of geologists 

 are too important as showing the connection between the two 

 great branches of natural science, not to encourage geologists to 

 further inquiry in the same direction, and it is with this object in 

 view that we have been led to the following reflections. 



We admit a similar geological (or chemical) constitution for 

 the various bodies of the solar system, and from this conclude that 

 the phenomena which have accompanied their formation and 

 their successive transformations must have been similar. Thus 

 the planets and satellites whose density is near to that of our 

 earth may be supposed to have passed through the dififerent 

 stages of liquid and solid incandescence, of the successive lique- 

 faction of portions of their gaseous envelopes, and to have finally 

 been the seat of an organic creation. 



Of these planetary bodies the best known to us is the moon, and 

 we shall now inquire to what extent our slight knowledge of it is 

 in accordance with the observations made on our earth, and with 

 the present state of the sun as supposed by Mr. Leverrier. It is 

 well known that astronomers, so soon as they became possessed of 

 good telescopes, discovered mountains and plains (or seas) on the 

 surface of the moon, and the immediate application of these names 

 shews the great resemblance which was supposed to exist between 

 the surfaces of the moon and the earth. It does not appear sur- 

 prising that the form of the lunar mountains should be met with 

 among only a small number of those on our planet, and physicists 

 easily explain the greater elevation and the steep declivities of the 

 former by the comparatively feeble action of the centripetal force 

 at the moon's surface. But one of the gravest objections to the 

 idea of a common origin of the moon and the earth is the appa- 

 rent absence of water and air from the surface of our satellite^ 

 thus seriously embarrassing those geologists who attribute terres- 

 trial volcanic phenomena to the intervention of these expansible 

 elements. 



If however we admit for the earth and the moon an identi- 



