3 i8 



THE POPULAR SCIENCE MONTHLY. 



an opportunity offers to examine a section of virgin soil and under- 

 lying strata, as occasionally happens on the bluffs facing the river, the 

 limit in depth of this black soil may be approximately determined. 

 Microscopical examination of it enables one to determine the depth 

 more accurately. 



An average, derived from several such sections, leads me to infer 

 that the depth is not over one foot, and the proportion of vegetable 

 matter increases as the surface is approached. Of this depth of super- 

 ficial soil probably not over one half has been derived from decompo- 

 sition of vegetable growths. Indeed, experiment would indicate that 

 the rotting of tree-roots yields no appreciable amount of matter. 

 While no positive data are determinable in this matter, beyond the 

 naked fact that rotting trees increase the bulk of top-soil, one archaeo- 

 logical fact we do derive, which is, that the flint implements known 

 as Indian relics belong to this superficial or " black soil," as Kahn 

 terms it. Abundantly are they found near the surface ; more spar- 

 ingly the deeper we go ; while below the base of this deposit of soil, 

 at an average depth of about two feet, the argillite implements occur 

 in greatest abundance. The accompanying diagram more clearly sets 



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forth the conclusions at which I have arrived, after years of careful 

 study of this subject. By this it will be seen that, as the depth 

 increases, the number of ordinary flint implements of Indian origin 

 decreases ; and that the reverse is true of the palaeolithic implements 

 which are a feature of the gravel-beds ; and is true of that inter- 

 mediate form which is characteristic of the stratum of sand capping 

 the gravels and blending insensibly with the surface-soil. This inter- 

 mediate form, which is always made of argillite, is both in workanm- 

 ship and design a marked advance over the palaeolithic implements, 

 and yet is so uniform in pattern and so inferior in finish, when 

 compared with the average flint implement of the Indian, that it has 



