FORMER GLACIATION OF WESTERN NORTH AMERICA. 355 



The evidence of former more extensive glaciation in South America is 

 qnite as uncertain as it is in regard to Africa. Darwin observed angular 

 fragments of granite on the island of Chiloe, which he thinks " might for- 

 merly have been floated across, on icebergs produced by the fall of glaciers."* 

 It is quite likely that there may have once been a larger development of the 

 ice masses at the southern end of South America ; and it Avonld seem reason- 

 able to suppose that the higher portions of the Chilian Andes might have 

 been occupied to some extent by glaciers, at a former period, in harmony 

 with what we have seen to be the case in the high ranges of corresponding 

 latitude north of the equator on the Pacific coast. But no trustworthy ob- 

 server has reported the existence of unquestionable traces of such former 

 glaciation, so far as known to the present writer. 



In a special section of the first chapter of this volume, imder the head of 

 " Former Glaciation of the Sierra Nevada, of the Pacific Coast, and of the 

 Cordilleras in General."! a sufficiently full description has been already- 

 given of the traces of the former presence of glaciers on the various ranges 

 on the western side of North America. Since only the highest portions of 

 the most elevated mountain chains were thus occupied — snow and ice 

 covering an area of at most a few hundred out of a million or more square 

 miles of territory within our own borders — it would seem that we can with 

 no more propriety use the term " Glacial epoch " in speaking of the period 

 of the former existence of glaciers in the Cordilleras, than we can in regard 

 to similar occurrences in Asia. There is, at all events, no evidence — 

 palfeontological, or of any other kind — that there has been any change 

 of climate on the western side of our continent since the Tertiary epoch, 

 other than that indicated by the ever-increasing desiccation, the proofs of 

 which have been brought forward in a former section. The disappearance 

 of the glaciers is simply another form in which the prevailing dryness has 

 manifested itself. 



We have thus passed in review the phenomena of past glaciation in 

 regions where — as it appears to the present writer — it is clear that the 

 (conditions are, and have been in former times, such that in order to account 

 ibr observed facts it is not necessary to invoke the aid of marked climatic 

 or topographical changes, or, indeed, of any agencies other than those in 

 harmony with the ideas maintained in the preceding chapters of this volume. 



* A'oyages rif llie Ailventure and Beagle, Vol. 111. p. 286. 

 t See ante, pp. 23-100. 



