1909- pRAEGKR. — Bota7iical Notes from Lough Mask, etc. 35 



The bold Boulder-clay scarps on the drift islands show a long 

 period of higher water-level, and the condition of the woods 

 on the broad foreshore on which the scarps look down points 

 to a considerable period during which the water has not 

 transgressed its present limits. So that all the evidence points 

 to a lowering of a long-persistent water level by natural causes, 

 probably some centuries ago, and to an extent of some 15 feet. 

 The lowering was, no doubt, caused by solution-enlargement 

 of water-passages through the limestone between L- Mask and 

 L- Corrib, allowing the drainage to proceed at a level lower 

 than before. The feature is a very interesting one^ and would 

 well repay study by a geologist. I am not aware of any simi- 

 lar feature among the other limestone lakes of Ireland. 



To return to the flora of the islands. On those that are 

 wooded, the line of the tree-tops rises at a small angle from the 

 windward to the leeward side, where the trees, 20 to 30 feet 

 in height, overhang the water (see fig. 2) — a feature very 

 characteristic of the island-flora of lakes in western Ireland. 



■l-^i^*. ■ • - 



Fig. 2. — Wind-moulded wood ou a Lough Mask island, seeu from the 

 north. 



The native trees consist chiefly of Ash, Oak, Birch, Holl}^ 

 Alder — the last colonizing the foreshore, and assisting the 

 bush-vegetation formed by Rhamnus catharticus and wallows, 

 with occasionally Ulex eitropcEus. Rhavinus Frangula is also 

 widespread ; it grows usually quite prostrate, with Riibus 

 ccesius, and more rarely R. saxatilis. Pimis sylvestris has been 

 planted on many islands, and sows itself in hundreds on the 

 .foreshores, not only of the planted islands, but of others also 

 both to east and west (leeward and windv/ard) of possible 

 parents. The undergrowth of the woods consists largely of 

 Geranium Robetiianuui and Circeea tutetiana, and sometimes of 

 Rubi, running down to the water's edge on the eastern sides. 

 The exposed western sides have a broadish, grassy, bushy, 

 block-strewn foreshore. Here Galium boreale, Eupatorium 

 ca7niabi7ium, Campanula rotu7idifolia, Solidago Virgaurea, 



