CAPPS: AGE OF THE LAST GREAT GLACIATION 



113 



terial making up a layer a foot thick around a living tree would be 

 considerably less than that thickness after it became deeply buried. 

 2. Toward the edge of the bluff, where the roots could be 

 best examined, the accumulation near the surface contains a 

 considerable admixture of wind-blown dust from the bare sand 

 and silt flat below. The deeper portions of the peat bed are 

 comparatively free from such extraneous material, and it is 

 probable that at the time they were laid down they were at 

 some distance from the bare gravel plain of White River. 



Fig. 4. Peat bluff, with angular, overturned blocks of peat and volcanic 

 ash. Photograph by F. H. Moffit. 



3. A considerable period of time probably elapsed after the 

 retreat of the ice before vegetation had completely established 

 itself upon the bared area of glacial till. Similarly, the ejection 

 of the heavy layer of volcanic ash, while it failed to kill the 

 spruce forest, doubtless destroyed the surface covering of 

 sphagnum moss, and this moss cover may have been a long 

 time in reestablishing itself. Even now there are on the moun- 

 tain front to the south large areas of bare ash, on which there 

 is only scanty vegetation. 



