1919] WATERMAN— ROOT SYSTEMS 25 



varies from i to 5 per cent. The dune sand is also characterized by 

 a very unequal distribution of organic material, in the presence not 

 only of old soil lines, but also of buried plant remains and of patches 

 and layers distinctly different in appearance and character from 

 the ordinary dune sand. The old soil lines, which are familiar to all 

 who have any acquaintance with dune regions, are usually quite 

 extensive, but generally appear only as a dark layer on the sloping 

 sides of blowouts. Only occasionally do they occur parallel to the 

 surface of the sand at such a depth as to affect the roots of annuals 

 or young perennials. The upper layers of the sand, however, are 

 generall}' characterized by the occurrence of layers of a dark color, 

 usually a few millimeters in thickness and covering less than a square 

 meter in area. The cause of the color has not been determined 

 definitely. It is apparently carbonaceous in nature, and its source 

 might be attributed to thoroughly decayed organic matter, and 

 sometimes also to unusual deposits of soot from steamers passing on 

 the lake. There is some evidence that this soot accumulates 

 on the snow in winter and is left on the sand when the snow melts 

 in the spring. It has been noticed also that in periods of extreme 

 dryness a very fine powder is formed from the attrition by the wind 

 of the exposed dead roots and stems of plants, and this is unevenly 

 distributed by the wind over large portions of the bare sand. When 

 fixed by a sudden shower and covered by later deposits of blown 

 sand, very thin interbedded dark layers might be produced. Other 

 layers and patches are marly in nature, and appear to have been 

 deposited in beds of dried pools in former pannes. Very rarely 

 patches of rusty color, giving an iron reaction, are found. They 

 are only a few centimeters in length and suggest a buried nail or 

 possibly a bit of meteoric iron as their cause. 



Glacial deposits. — The upper layers of the glacial deposits are 

 composed mainly of outwash material, sand with a few pebbles and 

 an occasional bowlder. They are generally covered with humus, 

 but in the crater blowout the erosion has been carried down to a 

 gravel layer. This differs greatly from the dune sand in physical 

 and probably in chemical constitution. 



Humus. — The forested dunes as well as the glacial deposits 

 are completely covered with a thin layer of leaf mold. This is 



