70 STUDIES FOR STUDENTS 



There may be false identifications of the overlying and under- 

 lying glacial deposits and of the interglacial beds themselves, and 

 there may be misinterpretations arising from that bete noire of the 

 incautious glacialist, secondary displacement and rearrangement, 

 but a duly trained and fairly skilful worker should avoid all 

 these. These interglacial beds present by far the most promis- 

 ing field for the demonstration of the presence of man in America 

 during the glacial period, if he really lived here then. No good 

 case of relics from them, however, has yet been presented, so 

 far as I know. 



III. EVIDENCES FROM ASSORTED DRIFT LYING UPON OR OUTSIDE 

 OF THE TRUE GLACIAL SERIES ; RIVER DEPOSITS ESPECIALLY. 



Nearly all the relics upon which the presence of man in 

 America in the glacial period has been claimed are from deposits 

 of this sort, and they hence deserve critical attention. For the 

 greater part, these deposits are valley trains or frontal aprons of 

 gravel, sand, and silt. There are three different classes of 

 deposits of this kind that are remarkably similar in their general 

 characters, but which must be positively distinguished from each 

 other before any safe conclusions can be drawn. This is a work 

 of grave difificulty, and in many cases I know of no way in which 

 it can be successfully done. One of these classes is glacial, and 

 the two others are postglacial. Before relics in these can be 

 referred to the glacial period, it must be shown that the deposit 

 bearing them belongs to the first class, and certainly does not 

 belong to either of the other two. 



1. The first class consists chiefly of gravel, sand, and silt 

 borne out from the ice by the glacial waters and deposited along 

 the glacial waterways. These are truly glacio-fluvial and strictly 

 contemporaneous with the ice action. Contemporaneous burial 

 in these means of course a glacial age. 



2. The second class consists of sand, gravel, and silt of almost 

 identical composition and structure formed by postglacial waters 

 working on the drift surface and washing out from it the same 

 class of material that the true glacial waters did and spreading 

 it along the valleys in an almost identical way. More than this. 



