64 Geological Society, 



not on celestial but terrestrial causes. The chapter that contains it 

 abounds in valuable information and ingenious reasoning 5 but when 

 the author tells us that* in every country " the land has been in some 

 " parts raised, in others depressed, by which and other ceaseless changes, 

 " the configuration of the earth's surface has been remodelled again and 

 " again since it was the habitation of organic beings, and the bed of the 

 " ocean lifted up to the height of the highest mountains," I cannot 

 but wish that he had stated this as an opinion, not as a fact. 



All these theories have one defect in common j they do not meet 

 the whole of the case. We have to explain not only the Cooling gra- 

 dual during the long interval that occurred between the formation of 

 the carboniferous beds and the chalk, but also the Sudden Chill which 

 followed, and seems to have continued from that time to this. There 

 is yet another element to be taken into account. The coal-beds of 

 Melville Island contain various plants, natives of the country where 

 they are found, and which, if we may trust analogy, require for their 

 healthy growth or for their growth at all, not only tropical heat t, 

 but a tropical apportionment of the periods of exertion and repose. 

 It is a botanical impossibility that such plants could have flourished in 

 a region in which they must have been stimulated by months of con- 

 tinuous Light, and paralysed by months of uninterrupted Darkness. 

 The distribution of Light, therefore, as well as of Heat, must formerly 

 have been different from what it is at present. 



To meet this further difficulty, recourse is had to physical astro- 

 nomy, which gives us the Precession of the Equinoxes, and a Shifting 

 Axis of Rotation : but the periodical changes of astronomers are insuf- 

 ficient to explain the phenomena to which I have just drawn your 

 attention. It has therefore been suggested that a greater change 

 may, in the course of ages, have been produced on the axis of the 

 earth's rotation by some foreign cause, say the Collision of a Comet. 



Such change is undoubtedly possible, but of possibilities there is no 

 end, and we must circumscribe our researches to render them useful. 

 Sir John Herschel gives us no encouragement, therefore, to proceed 

 with this speculation. Mr. Conybeare also dissuades us from it, but 

 by an argument which to me at least appears inconclusive. 



His argument, founded upon the lunar theory, is this, — that the 

 internal strata of the earth are ellipses parallel to its external out- 

 line, their centres being coincident, and their axes identical with that of 

 the surface. The present axis of the earth must therefore have been 

 its axis from the beginning. It may have been so, yet I should like 

 to be told by what process the form of the internal strata of the earth 

 had been so nicely determined. Possibly, however, I may not under- 

 stand the expression " internal Strata." All I believe to be ascer- 

 tained is, that of corresponding sections of the interior the density is 

 nearly the same, and if so, my inference is, not that the earth has 



* Principles of Geology, vol. i. p. 113. 



f Since this passage was written, doubts have been expressed whether the 

 specimens of these plants preserved at the British Museum are sufficiently 

 distinct to warrant the inference. 



