288 ANNUAL OF SCIENTIFIC DISCOVERY. 



such n distribution of the land and water as would account tor the observed 

 phenomena. Oihers again liave supposed a higher temperature in all parts 

 of the earth, derived from the central heat of the globe, and everywhere 

 producing contemporaneous similar faunas and floras. 



Without here entering upon the discussion of these views, I believe there 

 are few geologists or naturalists who accept these explanations of the causes 

 of the changes in climate as in any degree satisfactory. I have constantly 

 had this problem before me, deeming it to be one of the very highest inter- 

 est in physical geology, and have long since arrived at the conclusion that 

 there was no possible explanation of the phenomena without the supposition 

 of a constant change in the position of the axis of the earth's rotation; and 

 I think there are other great facts in physical geology which cannot be 

 explained under any other supposition. 



The question we have to consider is, whether there may not have been, 

 during those vast periods of the earth's history which geology unfolds to us, 

 some causes in operation which may have produced the supposed changes 

 in the position of the poles of the earth; and it appears to me that if we 

 take for our guide the investigations of Newton upon the effects which a 

 redundancy of matter on any point of the earth's surface must necessarily 

 produce, they will lead us to the conclusion that there must formerly have 

 been changes in the position of the poles, with the consequent changes of 

 climate on every part of the earth. 



I assume, as an admitted fact, that the mass of the earth was at first a 

 fluid mass, and that it is at present a fluid mass with a hardened crust, and 

 that the present oblate form of the earth is due to its rotation on its axis; 

 and that if we suppose any cause which would tend to produce a change in 

 the position of the poles, the mass of the earth was at all times, and is still, 

 free to assume the new form which its revolution on a new axis would tend 

 to produce, but with certain changes in the hardened crust, to which I will not 

 further allude than to say I refer to what is called " slaty cleavage," which, 

 passing through vast masses of rocks, which are spread over large areas, 

 has split up the rocks intolaminre as fine almost as the imaginary fluxional 

 increments of the mathematician, and also to the vast number of "faults" 

 by which the rocks forming the crust of the earth are broken up, and to the 

 undulations of the strata in nearly parallel folds over large areas. Every 

 geometrician must sec that this is precisely such a result as might be ex- 

 pected under the supposition of a change in the position of the poles, with a 

 corresponding change in the form of the earth. To take a simple illustra- 

 tion : if we hold a thick book between the hands, and imagine the surface 

 formed by the edges of the leaves to represent the surface of a homogeneous 

 mass of rock, such as that out of which slates are formed, and we then 

 depress one side of the book so as to make the surface slightly inclined to its 

 original position, it will be seen that an almost infinitesimally small sliding 

 movement is given to each leaf, and that this represents what must take 

 place under the hypothesis in a homogeneous rock, and produce the "slaty 

 cleavage." If, again, we place a number of books side by side on the 

 ground, and then push them on one side, it will be observed that each book 

 will slide, to a certain extent, over the one beneath it, and that this disloca- 

 tion will represent the " faults" which occur through any compound scries 

 of strata, such as the coal-measures, and it will be observed that the displace- 

 ment is down the inclined plane, as is always observed in the "faults." The 

 struia in each case arc supposed to have been originally horizontal. 



