Dr. James Croll — On Geological Time. 391 



•universal that we must refer the climatic changes in question to some 

 cosmical cause. 



The theory of a change in the obliquity of the ecliptic has been 

 appealed to. This theory for a time met with a favourable reception, 

 but, as might have been expected, it was soon abandoned. The re- 

 searches of Mr. Stockwell of America, and of Mr. George Darwin and 

 others in this country, have put it beyond doubt that no probable 

 amount of geographical revolution could ever have altered the obli- 

 quity to any sensible extent beyond its present narrow limits. It has 

 been demonstrated for example, by Mr. George Darwin, that supposing 

 the whole equatorial regions np to lat. 45° N. and S. were sea, and 

 the water to the depth of 2000 feet were placed on the Polar regions 

 in the form of ice — and this is the most favourable redistribution of 

 weight possible for producing a change of obliquity — it would not 

 shift the Arctic circle by so much as an inch I 



Variations in the obliquity of the ecliptic having been given up as 

 hopeless, geologists and physicists are now inquiring whether the 

 true cause may not be found in a change in the position of the earth's 

 axis of rotation. Fortunately this question has been taken up by 

 several able mathematicians, among whom are Sir William Thomson,^ 

 Professor Haughton,^ Mr. George Darwin,^ the Eev. J. F. Twisden,* 

 and others ; and the result arrived at ought to convince every 

 geologist how hopeless it is to expect aid in this direction. 



Mr. George Darwin has demonstrated that in order to displace 

 the pole merely 1° 46' from its present position, 2V of tbe entire 

 surface of the globe would require to be elevated to a height of 10,000 

 feet, with a corresponding subsidence in another quadrant. There 

 probably never was an upheaval of such magnitude in the history of 

 our earth. And to produce a deflection of 3° 17' (a deflection which 

 would hardly sensibly affect climate) no less than -^ of the entire 

 surface would require to be elevated to that height. A continent ten 

 times the size of Europe elevated two miles would do little more 

 than bring London to the latitude of Edinburgh, or Edinburgh to 

 the latitude of London. He must be a sanguine geologist indeed 

 who can expect to account for the glaciation of this country, or for 

 the former absence of ice around the poles, by this means. We know 

 perfectly well that since the Glacial Epoch there have been no changes 

 in the physical geography of the earth, sufficient to deflect the pole 

 half-a-dozen miles, far less half-a-dozen degrees. It does not help 

 the matter much to assume a distortion of the whole solid mass 

 of the globe. Tiiis, it is true, would give a few degrees additional 

 deflection of the Pole ; but that such a distortion actually took place 

 is more opposed to geology and physics than even the elevation of a 

 continent ten times the size of Europe to a height of two miles. 



Mr. Twisden, in his valuable memoir referred to, has shown even 

 more convincingly how impossible it is to account for the great 



1 Britisli Association Eeport, 1876 (part 2), p. 11. 



2 Proceedings of Royal Society, vol. xsvi. p. 51. 



3 Transactions of Royal Society, vol. 167 (part 1). 

 '^ Quart. Journ. Geol. Soc. February, 1878. 



