9 12 Proceedings of the Royal Irish Academy. 



known about them. Where definite root-layers occur in the peat, however, 

 the lower ones invariably appear to lie at about the level of the existing water- 

 table or rather below it, while the upper layer lies within 3 or 4 feet of the 

 water-table, and just below the Sphagnum or red bog. It is usually difficult 

 to identify the true water-table of many bogs, owing to the holes cut and left 

 in the peat by turf-cutters ; but it may be assumed that the water lying in 

 bog holes during the summer is, if anything, rather below than above the 

 natural water-table, the latter having been lowered by drainage. The root- 

 layers are evidently the remains of several generations of trees, for two or 

 three large roots may be found resting immediately above each other, showing 

 that the upper originated as seedlings upon the decayed stumps of the lower ; 

 and for these successive stages of growth and decay to have taken place a 

 period of 500 to 1000 years would be required. Another feature of these 

 stump-layers is that while the lower edge is frequently indefinite, and at no 

 precise level, the upper edge finishes off along a more or less horizontal 

 line, as if the trees had ceased to grow at one particular period. The roots 

 themselves, especially the larger ones, are extended horizontally in all 

 directions, but seldom show any trace of a descending tap or side roots, or even 

 roots running obliquely downwards as is the case with Pine growing on well- 

 drained porous soil. This flat root system suggests a water-logged condition 

 1 foot or 18 inches below the surface ; and, furthermore, that this water- 

 logging was due to a water-table at a fixed level. Had the bog gradually become 

 drier, as suggested by Sernander and others, the trees would have ultimately 

 sent down " sinkers," or perpendicular roots, as is the case when Pine is 

 planted on artificially drained bog, with a gradually sinking water-table. A 

 significant fact is the occurrence of the upper root-layer invariably below the 

 Sphagnum peat, and near the upper surface of the black marsh peat, showing 

 that the change which killed off the last layer of trees was also accompanied 

 by a change in the composition of the bog, and was not necessarily due to an 

 increase of moisture alone. The under edge of this Sphagnum peat often 

 shows layers of Sphagnum which have been bent or pressed down on either 

 side of the pointed end of a stump, showing that its rate of growth was 

 comparatively rapid, and that it followed a period during which the peat on 

 which it rests was of a different character, and had attained a firm surface. 



Another conclusive proof of the marked chemical difference between the 

 black peat bearing stump-layers, and the red or Sphagnum bog above, is found 

 in the rate of growth of the bog-timber. However well high bog may be 

 drained by natural or artificial agencies, the growth made by Pines or other 

 trees is invariablj' slow after the first ten or fifteen years, and the maximum 

 size such trees attain is seldom more than 12 inches in diameter at breast 



