114 CAPPS: AGE OF THE LAST GREAT GLACIATIOIST 



4. According to F. V. Coville, trees of very slow growth fail 

 during unfavorable years to form distinct annual rings, and 

 therefore the age of the tree, as shown by a count of the rings, 

 may be considerably greater than the figures obtained. From 

 the same authority comes the statement that during the first 

 years after germination the spruce tree grows very slowly, so 

 that a count of the rings made 4 feet above the present sur- 

 face, or say 6 feet above the lowest horizontal roots, would 

 fail to show the first 20 years or so of the tree's growth. 



Sound trees so situated that their roots could be studied, 

 and ring counts made, were not easily found, and in only one 

 instance was the count made on a tree which seemed to have 

 developed under conditions which approached the average. 

 On this tree one count, made 6 feet above the present sur- 

 face of the ground, where the tree had a diameter of 7| inches, 

 showed 373 annual rings. At 8 feet above the ground another 

 count was made as a check and gave 362 rings. This tree had 

 an accumulation of 24 inches of vegetable matter above its 

 lowest horizontal roots. With an allowance of 27 years for 

 the growth of the tree up to the point where the count was 

 made, a rate of accumulation of the vegetable material of about 

 1 foot in 200 years was obtained. In the peaty material around 

 the roots of this tree there was considerably more wind-blown 

 sand and silt than in the peat exposed below. Another count, 

 made on a tree 5| inches in diameter, gave 133 rings, and the 

 roots had 16 inches of very sandy peat about them. The un- 

 usually sandy condition of the peat about this tree must indicate 

 an unusually rapid burial of the tree, and consequently the 

 figures of the rate of accumulation are too small to be gener- 

 ally applied. Emphasis is again placed upon the fact that the 

 surface peat is much less solidly compacted than that more 

 deeply buried, and the figure on which most confidence is placed, 

 namely 200 years to the foot of peat, is doubtless much less 

 than the actual number of years required for the average foot 

 of peat to accumulate at this place. 



Disregarding, therefore, many unweighed factors, all of 

 which would tend to give a slower rate of accumulation, and 



