396 ALTERNATE GLACIAL PERIODS 



found by Dr. Hooker on widely separated mountains m 

 this island tell the same story of a former cold period. 

 From facts communicated to me by the Eev. W. B. 

 Clarke, it appears also that there are traces of former gla- 

 cial 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 latitude thirty-six and 

 thirty-seven degrees, and on the shores of the Pacific, 

 Avhere the climate is now so different, as far south as lati- 

 tude forty-six degrees. Erratic bowlders 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 Chili I 

 examined a vast mound of detritus with great bowlders, 

 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 latitude thirteen to thirty degrees south, at about the 

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

 those with which he was familiar in l^orway, and likewise 

 great masses of detritus, inchiding grooved pebbles. Along 

 this whole space of the Cordillera true glaciers do not now 

 exist even at much more considerable heights. Further 

 south, on both sides of the continent, from latitude forty- 

 one degrees to the southernmost extremity, we have the 

 clearest evidence of former glacial action, in numerous 

 immense bowlders transported far from their parent 

 source. 



From these several facts, namely, from the glacial action 

 having extended all round tlie northern and southern 

 hemispheres — from the period having been in a geological 

 sense recent in both hemispheres — 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 gla- 

 ciers 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 tempera- 

 ture 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 



