66 STUDIES FOR STUDENTS 



primarily in the glacial formations themselves. This is the 

 principle we recognize in the assignment of a pebble or a 

 bowlder, and it should hold good for human relics. A few years 

 ago two of our most experienced glacialists and three younger 

 associates reconnoitered seven states, and then held their con- 

 clusions in abeyance for several years, because they were not 

 fully convinced that certain crystalline pebbles in certain gravels 

 outside the true glacial formations were or were not truly glacial 

 in origin. Had these pebbles been found in glacial deposits, 

 their reference would not have caused a moment's hesitation. 

 It is only applying to human relics the standards adopted by 

 careful glacialists relative to pebbles, to insist that there is a 

 profound distinction between the value of evidence from the 

 direct glacial deposits and that from derivatives or secondary 

 deposits. 



I. EVIDENCE FROM PRIMARY GLACIAL DEPOSITS. 



There are three good classes of cases connected with the 

 primary glacial material : 



I . The first of these is imbedment i?i the till sheets or the moraines. 

 If the identification of the glacial deposits and of the relics be 

 beyond question, relics found imbedded in the true glacial 

 deposits constitute very strong evidence of contemporaneous or 

 previous origin. There is some danger of error even here, how- 

 ever. Secondary deposits of till are liable to be confused with 

 true original deposits. Slides, creep, and wash not infrequently 

 bury recent material under what at first seems to be true 

 bowlder clay. Many a time has the experienced and alert 

 glacialist had occasion to use the most careful circumspection 

 to avoid error in assigning wood, buried soils, and other fossils 

 to a glacial or interglacial age, whose burial proved on close 

 inspection to be secondary and utterly worthless for chronolog- 

 ical purposes. There are also incidental intrusions by means 

 of burrows, root holes, cracks, etc., which require elimination. 

 If all these are excluded by expert observation controlled by unre- 

 laxijig alertness a?id persistent cautioii, evidence of a high order of 

 value is theoretically derivable from the tills and the moraines. 



