While investigating the problem of coastal changes in South Wales, and examining 1 the area of the Merthyr Mawr Warren (Fig. 1) for this purpose, the differences, observable in the surface conditions to-day, and evident in the records of the past, between the areas east and west of a line approximating to the Burrows Well stream, suggested that the relatively recent physical history of the two sections of the area had not been similar. The greater width in the east suggested recent accumulation in this section, and the presence of what appeared to be successively formed littoral dunes pointed to a relatively recent phase of prograding, while the topography made it possible that these changes were related to the mouth of the River Ogmore.