Clare Island Survey— Tree-Growth. 9 13 



height. In the root-layers, many piues show a rapid rate of growth during 

 the first fifty or sixty years, and rings from one-fifth to one-tenth of an inch 

 in breadth are common. The large size attained by many of the bog trees is 

 well known, although an exaggerated idea of this may be easily gained from 

 the horizontal root system. However, there is no reason to doubt that trees 

 of 2 to 3 feet in diameter at breast height existed. A Pine in the lower 

 group of bogs on Clare Island showed fifty rings in the first 12 inches of 

 radius, the broadest ring being a quarter of an inch wide. This rate of growth, 

 together with the frequent occurrence of Oak on bogs throughout Ireland, 

 proves that the peat in which the trees grew had comparatively little acidity, 

 whereas the acidity of the Sphagnum bog is well known, and invests the bog 

 flora with a distinctly xerophytie character. The occurrence of Oak of 

 comparatively large size in the root-layers proves the favourable chemical 

 condition of the peat, as Oak never attains a large size on sour bog. 



The problem of peat with and without root-layers is not, therefore, a 

 mere question of moisture or drainage, but probably one connected with the 

 character of the soil-water. Many facts point to the same changes in the 

 level of the water-table having taken place, as is suggested by the Clare 

 Island tree-remains, and render it highly probable that periodic increases 

 and decreases in the flow of springs feeding the bogs occurred, bringing about 

 a submergence of the tree-growth on peat, and a renewal of the marsh 

 growth, the trees again spreading over the bogs when the level of the marsh 

 had again become stationary. For this to have occurred, it is necessary 

 to assume that the majority of bog areas had no definite drainage outlet 

 in earlier times, otherwise a mere increase or decrease in the supply 

 would not permanently alter the level of the water-table beyond a few 

 inches, provided the supply was not too small to make good the loss from 

 evaporation. "While it is not impossible that the latter occurred, the flat- 

 root system of bog-timber rather favours the theory of a stationary than a 

 falling water-table during the period of tree-growth. 



This assumed rise in the water-level of bogs and lakes is borne out in 

 other directions. The majority of the crannogs existing throughout Ireland 

 have been discovered after the lowering of lakes by arterial drainage. Many 

 of these crannogs also rest upon peat, and are now covered by considerable 

 depths of bog ; and it is quite reasonable to assume that a certain amount of 

 subsidence has occurred since many of the crannogs were last inhabited. But 

 those which have appeared after the lowering of lakes usually stand upon 

 islands and solid foundations, and these could not have sunk to any appreciable 

 extent, but must have been submerged after they were built, and probably 

 since they were last inhabited. Possibly the silting up of streams and the 



