CRITERIA REQUISITE TO A GLACIAL AGE 83 



the glacial deposits cannot usually be correlated with the glacial 

 stages so definitely by stratigraphic or other physical means as 

 to furnish unquestionable evidence of their glacial age. In spe- 

 cial cases it may be possible, but these cannot well be treated 

 here. The question is, however, pertinent whether palaeonto- 

 logical evidence cannot bring these outlying non-glacial deposits 

 into sure correlation, as it does in other parts of the geological 

 column. It is certainly to be presumed that palaeontology can 

 do for the Pleistocene period what it has done for earlier ages, 

 but the real question is whether this meets the minute require- 

 ments of the question in hand. Has paleontology at any stage 

 reached a degree of refinement that enables it to discriminate 

 surely between stages of the order of the glacial epochs by the 

 use of criteria developed in other regions tha?i those immediately coti- 

 cerned? It will not be questioned that when the faunas and 

 floras of each of the glacial stages in America have been well 

 worked out and demonstrably connected with those stages, and 

 when it is shown by ample evidence that certain species lived in 

 America in certain stages, and not in others, the criteria so deter- 

 mined can be used in confident correlation ; but these criteria must 

 first be demonstrated to be true criteria in their American applicatio?i. 

 General inferences as to the rate of evolution or the rate of 

 extinction are not sufficiently refined for the purposes of this 

 case, without such specific local demonstration. General infer- 

 ences and faunal aspects may be applicable to periods measured 

 by hundreds of thousands or millions of years, and yet be quite 

 too broad to discriminate epochs of a few thousands or even tens 

 of thousands of years. The historical period of eight or ten thou- 

 sand years gives little basis for confidence in palseontological 

 refinements of this latter order; certainly not until their specific 

 trustworthiness in a given application is demonstrated. Here as 

 everywhere else in the geological column the range and limita- 

 tion of species must be demonstrated stratigraphically before 

 the occurrence of these species can be used to fix horizons and 

 determine correlations except in a general and tentative way. 

 The palaeontology of the American glacial series is yet to be 

 developed in the main. It is known that many species survived 



