512 GEOLOGY. 



full assurance that the particular portion involved was not shifted. Because 

 of this fundamental difficulty, and of the great liability to misinter- 

 pret the secondary burials previously described, and because of some 

 other contingencies we cannot here discuss, 1 it is scarcely possible 

 to make out a good case of proof of contemporaneity with an ice stage, 

 from relics found in river gravels, unless the inherent evidences con- 

 nected with the relics themselves are altogether convincing. 



All surface formations, however perfect their integrity in other 

 particulars, are subject to surface disturbances, and to the intrusion 

 of surface objects, through (1) the overturning of trees, (2) the pene- 

 tration of roots, their subsequent decay, and the filling of the root- 

 holes, (3) the burrows of animals, (4) earth-cracks developed by 

 drouth, and various other incidental agencies. Wind-blown dust and 

 sand also bury surface objects. All loose formations, glacial or other- 

 wise, are subject to secondary modifications in these and other ways, 

 to degrees and extents only appreciated by special students of such 

 phenomena. 



There is a rather important class of recomposed formations made 

 by the shifting or rehandling (by eolian, pluvial, fluvial, slumping, 

 and other processes) of drift, loess, or alluvium, which so closely simu- 

 lates the original formations of like class as to deceive geologists of no 

 little experience. Some of the supposed evidences of man's antiquity 

 that seem, on their faces, to be strongest, are but cases of burial beneath 

 such recomposed formations of comparatively recent date. Occasional 

 burials of relics to depths of many feet may, therefore, carry little 

 weight. 



Sources of good evidence. — There are two classes of formations in 

 which good evidences of glacial man, if there was such man in America, 

 are to be sought, viz., (1) in undisturbed till-sheets below horizons 

 affected by surface intrusion, and (2) in interglacial beds, where over- 

 lain by till and protected from all assignable sources of subsequent 

 intermixture. Poth these classes of beds have yielded fossils of other 

 forms of life, and these alone have been seriously considered in the 

 usual studies of the life of the glacial and interglacial stages. These 

 beds have not yet yielded human relics in America, but they should 

 do so in time, if man was a member of the faunas of glacial or inter- 

 glacial times. 



1 Jour, of Geo!., XI, 1C03, pp. 74-75. 



