112 CAPPS: AGE OF THE LAST GREAT GLACIATION 



ply from the lowest roots and caused the tree constantly to 

 throw out new sets of roots near the surface, in its efforts to 

 survive. If these premises are correct, then the vertical dis- 

 tance between 'the lowest horizontal roots of a tree and the 

 surface of the ground represents the thickness of the peaty 

 accumulation during the growth of the tree, and the rate of 

 accumulation can be determined by ascertaining the age of the 

 tree, as shown by the annual rings. 



It is readily admitted that any figures for the rate of accu- 

 mulation of peat, obtained in the way outlined are subject to 



Fig. 3. Close view of an overturned block of peat, with included spruce 

 stumps. 



many uncertainties, and before they can be considered final 

 should be checked by a much larger number of measurements 

 than could be made in the single day which was available for this 

 study. Most of the qualifying factors, however, seem to fall 

 on the side of conservatism, and to give a minimum, rather 

 than a maximum figure. Among the unweighed factors the 

 following may be briefly mentioned: 



1. The vegetable matter accumulating near the surface is 

 less compact than that deeper in the section, so that the ma- 



