Pethybuidge & Praeger — Vefjetation South of JDtih iin. 165 



We have, therefore, in our Sci'rpus association one in which peat 

 is still being formed at the present time, and it is from this association 

 almost solely, in our area, that peat is cut for fuel ; so much so that 

 when we saw a dotted road amongst the moors shown on the map, we 

 were practically certain on reaching its branching ends to find ourselves 

 in the midst of this association. It is at these points, too, as mentioned 

 before, that we find that, owing to the improved drainage caused by 

 turf-cutting, the bog ceases to grow, and becomes invaded by the 

 Calluna association. 



Without doubt peat, too, is being accumulated at the present day 

 in the Erioyliorum areas wliich we shall presently describe ; but, as a 

 rule, these are on much higher ground, and, consequently, not so 

 accessible as the Scirpus areas for turf-cutting. 



In former times, doubtless, these two peat-forming associations 

 were spread far and wide over the mountains in our district, and we 

 believe that the thick caps of peat on our mountain summits were 

 probably formed in this way. At the present day, however, owing to 

 altered climatic conditions, and especially to the improved drainage 

 both above and below ground, not only are the peat-forming plant 

 associations absent, but even the Calluna associations present are, 

 with great difficulty, struggling to hold their own against the denuding 

 agents which are carrying oJffi the surface vegetation and the under- 

 lying peat, leaving a wilderness of devastation behind. 



We have not found time to examine the peat deposits in any 

 detail for evidence of the climatic conditions of former days, but 

 we may mention that in these peat areas we have found remains of 

 trees such as Scots Pine and Birch at about 1250 and 1700 feet, 

 respectively. 



To return to the plants of which the association is composed, all 

 of them show well-marked xerophytic characters. The reasons for 

 this are not at once obvious, as it would seem unnecessary for plants 

 living in such wet places to take special precautions against excessive 

 transpiration. A wet soil, however, is a cold one ; and it is possible 

 that the difficulty of absorption by the roots, owing to the low 

 temperature of the soil, caused not only by the presence of water in it, 

 but also by the evaporation taking place during the strong winds in 

 spring, coupled with tlie drying tendency of the winds themselves on 

 the overground parts, results in the presence of plants with drought- 

 resisting characters. 



Again, we kuow the tenacity with which peat holds water; and it 

 is possible that this is so great that the living plants have difficulty 



