Clare Island Survey — Tree-Growth. 9 1 1 



the soil or bottom of the bog was regarded as a proof of its later origin, the 

 fact being overlooked that the Pine horizon was lower than that of the Oak, 

 and, therefore, older, and not younger. 



With regard to the root-layers, considerable difference of opinion exists in 

 the minds of Continental investigators as to their occurrence and cause. That 

 the stumps of trees are found in definite layers, separated by two or three 

 feet of peat free from roots, is well known ; but as their distribution in any 

 bog can be seen only where they are exposed at the turf banks, and records 

 of those previously found in the peat are either wanting or based on hearsay, 

 how far they extend on a definite horizon is difficult to say. No difficulty 

 appears to arise in tracing them over an area of two or three acres in many 

 bogs ; but when larger areas are dealt with, the difficulty arises of making 

 sure that peat of the same age is being investigated at one place as at another. 

 But, assuming that these root-layers exist — and this is beyond all doubt so far 

 as limited areas are concerned — their origin is a matter of considerable interest. 

 Swedish bog-investigators are sharply divided in their opinions on this point, 

 one theory being that they represent a climatic change from wet to dry 

 conditions, the other favouring the idea that a local change in the condition of 

 the bog may account for them. Sernander and Andersen are the principal 

 exponents of these respective theories ; the former advocating the climatic 

 theory, the latter the local or " edaphic " explanation. 



Lewis' states that " all the Scottish peat mosses show a definite succession 

 of plant remains. The oldest, in the South of Scotland and the Shetland 

 Islands, have an arctic plant-bed at the base. This is succeeded by a forest 

 of Birch, Hazel, and Alder, containing temperate plants. A second arctic 

 plant-bed occurs above the lower forest, and is overlaid in all districts (except 

 the Hebrides, Cape Wrath, and the Shetland Islands) by an Upper Forest 

 covered by several feet of peat bog plants." The Upper Forest appears, 

 according to Lewis, to consist of Pine, in one or two root-layers, separated, 

 in the latter case, by two to three feet of peat. If the same succession holds 

 good in Ireland, it is evident that the Lower Forest is invariably hidden 

 beneath the water-table. In the vicinity of many bog sections which show 

 no trace of stumps above the water-table, fragments of Birch are taken up by 

 peat diggers; but whether Hazel and Alder are also present is a matter for 

 further investigation. 



As far as Ireland is concerned, it would appear that root-layers are chiefly 

 confined to the smaller bogs, or to the margins of the larger ones, although 

 in the case of the latter the deeper peat-layers are invisible, and little is 



1 Trans. Koy. Sue. Edinb., vol. xlvi, Part I (No. 2). 



B2 



