2IO THE SCOTTISH BOTANICAL REVIEW 



area of this sheet of water is 68 acres, and its greatest depth is 

 1 1 feet. The water is fresh and fed by springs on the landward 

 side. It has existed in its present form since 1876, but is of less 

 extent and slightly different outline to the pool of 1814. It was 

 originally a marsh, and its eastern margin is still, in part, character- 

 ised by a marsh vegetation. At that time it was drained by a stream 

 which flowed in a northerly direction and emptied itself into Kenfig 

 river. To-day there is no visible outlet, but it is possible that its 

 waters filter through the sand and ultimately enter the river in 

 that way. 



Geology^ Climate, and Rai?ifalL 



The blown sand rests on the Keuper marls of the Trias formation. 

 Rocks which project here and there through the sand nearly all con- 

 sist of conglomerate, which is more or less calcareous in composition. 

 The wedge of land which has the pool as its apex is boulder clay 

 resting on Triassic conglomerate, while the southern boundary of the 

 "white" dunes is of like glacial origin. A broad stretch of alluvium 

 marks the northern limit, and an irregular alluvial tract extends from 

 the margin of the pool to within a short distance of the shore. The 

 climate is mild and humid. Owing to the prevalence of warm 

 south-westerly winds the mean January temperature is about 41° F., 

 and it is probable that the resultant mild winters have a modifying 

 effect upon the vegetation. The corresponding July temperature is 

 62° F. The average annual rainfall, estimated over a number of 

 years, is a little over 33 inches. The wettest months of the year 

 are July to January inclusive. A complete analysis of the soil and 

 sand taken from different stations on the dunes is now being carried 

 out, and a detailed account of soil conditions will be embodied in a 

 future publication. Cattle and horses are pastured on the dunes, 

 and the soil is thus enriched with manure. Molluscan shells are 

 abundant in many of the hollows. 



The plant formation which covers this area is a natural one, and 

 presents many interesting biological features. A comprehensive 

 ecological study of its vegetation, on modern lines, is now being 

 undertaken, and it is hoped to extend this investigation so as to 

 include the entire belt of sand dunes from Porthcawl to Swansea. 

 So far, detailed observations have been chiefly confined to the 

 Kenfig district. This communication is, therefore, not intended to 

 be exhaustive, and is merely a brief account of the more salient 

 features of the vegetation. 



The Plant Associations. 



The three most prominent and well-marked associations in this 

 formation are the following: i. The association of AmmopJiila 

 arenaria; 2. the association of Salix repens ; 3. the association 

 of Pteris aquilina. 



I. The association of Ammophila arenaria. — This association is 



