CHAP. XII.] IN THE NORTH AND SOUTH. 315 



Sikkim, Dr. Hooker saw maize growing on ancient and gigantic 

 moraines. Southward of the Asiatic continent, on the opposite 

 side of the equator, we know, from the excellent researches of 

 Dr. J. Haast and Dr. Hector, that in New Zealand immense 

 glaciers formerly descended to a low level ; and the same plants 

 found by Dr. Hooker on widely separated mountains in this 

 island tell the same story of a fonner cold period. From facts 

 communicated to me by the Rev. W. B. Clarke, it appears also 

 that there are traces of former glacial action on the mountains of 

 the south-eastern corner of Australia. 



Looking to America ; in the northern half, ice-borne fragments 

 of rock have been observed on the eastern side of the continent, 

 as far south as lat. 36-37, and on the shores of the Pacific, where 

 the climate is now so different, as far south as lat. 46. Erratic 

 boulders have, also, been noticed on the Rocky Mountains. In 

 the Cordillera of South America, nearly under the equator, glaciers 

 once extended far below their present level. In Central Chile I 

 examined a vast mound of detritus with great boulders, crossing 

 the Portillo valley, which there can hardly be a doubt once 

 formed a huge moraine ; and Mr. D. Forbes informs me that he 

 found in various parts of the Cordillera, from lat. 13 to 30 S., at 

 about the height of 12,000 feet, deeply-furrowed rocks, resembling 

 those with which he was familiar in Norway, and likewise great 

 masses of detritus, including grooved pebbles. Along this whole 

 space of the Cordillera true glaciers do not now exist even at 

 much more considerable heights. Farther south on both sides of 

 the continent, from lat. 41 to the southernmost extremity, we 

 have the clearest evidence of former glacial action, in numerous 

 immense boulders transported far from their parent source. 



From these several facts, namely from the glacial action having 

 extended all round the northern and southern hemispheres from 

 the period having been in a geological sense recent in both hemi- 

 spheres from its having lasted in both during a great length of 

 time, as may be inferred from the amount of work effected and 

 lastly from glaciers having recently descended to a low level 

 along the whole line of the Cordillera, it at one time appeared to 

 me that we could not avoid the conclusion that the temperature 

 of the whole world had been simultaneously lowered during the 

 Glacial period. But now Mr. Croll, in a series of admirable 

 memoirs, has attempted to show that a glacial condition of 

 climate is the result of various physical causes, brought into 

 operation by an increase in the eccentricity of the earth's orbit. 

 All these causes tend towards the same end; but the most 

 powerful appears to be the indirect influence of the eccentricity 

 of the orbit upon oceanic currents. According to Mr. Croll, cold 

 periods regularly recur every ten or fifteen thousand years ; and 



