9 14 Proceedings of the Royal Irish Academ//. 



formations of bogs may have temporarily raised the level of lakes from time 

 to time, but the natural deepening of a drainage-channel is quite as common 

 an occurrence, and the level of every lake cannot have been raised by silt or 

 peat-formation. 



In many parts of Ireland, again, tree stumps can be seen below the 

 present level of the water, and the same thing has been noticed in Sweden. 

 Wright 1 has observed these submerged stumps in Donegal, and points out 

 the impossibility of their submergence being due to any tilting of the earth's 

 crust which might alter the drainage outflow. In some instances, however, 

 it is quite possible that these lakes were originally peat bogs, and the stumps 

 now remaining are simply the residue of the bog which has been gradually 

 eaten away by a stream which has increased in volume during comparatively 

 recent times, and subsequent to the growth of the trees on the peat. This 

 erosive or corrosive action of spring-water upon peat is clearly demonstrated 

 in many parts of Ireland by the green lines which intersect stretches of 

 mountain peat, due to streams which have cut their way through two or three 

 feet of peat, and leaving the edges in the form of perpendicular walls along 

 the line of flood- water mark. The course of many of these streams could not 

 have been materially altered since the peat-formation took place, and the 

 most reasonable conclusion is that precipitation has increased within com- 

 paratively recent times. Bog-slides and surface denudation of peat in 

 mountain districts point in the same direction. 



Another link in the chain of evidence regarding this point is the almost 

 invariable position of the uppermost root-layer with regard to the water- 

 table, and the existence of the lower one on or below the latter. Had all lakes 

 in which bogs have since formed been at a fixed level from the beginning, the 

 occurrence of the lower root-layer would have been impossible, or the upper 

 one could not have become submerged for any length of time. Although the 

 general subsidence and consolidation of the peat might possibly have brought 

 about the death of one root-layer, the probabilities are that had this occurred 

 a continuous series of stumps would be present, corresponding to the surface 

 of the marsh, until the latter gradually became converted into Sphagnum 

 peat. 



The probable periods of time which have elapsed since the Pine, Pine and 

 Oak, and Oak respectively flourished on Clare Island and the mainland 

 cannot be given with any degree of accuracy. Various estimates have been 

 made of the length of time required to form a certain depth of peat, but all 

 are based upon such uncertain data that they must be regarded as unreliable. 



1 Geological Mueazine, N.S. Ducu.de V, vol. ix. 



