80 TRANSACTIONS OF THE [Sess. lxxvi. 



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 Rainfall. 



The blown sand rests on the Keuper marls of the Trias 

 formation. Rocks which project here and there through 

 the sand nearly all consist 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 corre- 

 sponding 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. 



