84 STUDIES FOR STUDENTS 



the earlier and more extensive ice invasions, and became extinct 

 either during the later stages or since the glacial period. It is 

 known that some species survived for some appreciable time 

 after the last glacial stage, and yet became extinct before the 

 American historical period, as, notably, the mammoth and mas- 

 todon. The fauna of which the mammoth and mastodon were 

 the elephantine types not unlikely bore an aspect measurably 

 different from that of the same region today, and, but for the 

 stratigraphic proof to the contrary, would undoubtedly be 

 regarded as evidence of rather high antiquity, as indeed was the 

 actual case before the recency of this fauna was demonstrated. 

 The association of man's relics with those of extinct animals merely 

 raises the Janus-faced question whether it means the antiquity 

 of man or the recency of extinction of the animals. General 

 considerations and Old World analogies are incompetent to 

 decide this question in America. It must be worked out by 

 specific stratigraphic and correlated evidences of a degree of 

 precision and refinement commensurate with the geologic 

 minuteness of distinctions involved in the problem. 



CONCLUSIONS. 



The foregoing analysis has not been carried into all the 

 refinements that special cases involve, but it has perhaps been 

 extended far enough to make clear the general fact that the 

 reliable reference of human relics to a glacial age is attended by 

 many possibilities of error, and that these can be avoided only 

 by the exercise of sagacity, guided by experience and controlled 

 by the most diligent circumspection. 



Promising grounds. — Two general classes of formations fur- 

 nish promising grounds for search, so far as their trustworthi?iess 

 is concerned, when critically studied, viz.: (i) the immediate 

 glacial formations, i. e., the till sheets and the moraines ; and (2) 

 the interglacial formations. 



Unpromisijig grounds. — -Certain other classes of formations are 

 so subject to error, or at least to the suspicion of error, that there 

 is very slight ground of hope that they will furnish incontestible 

 evidence, and hence cases founded on these formations should 



