54 DR T. J. JEHU ON 



On the south coast of Lleyn there are indications that during some pre-glacial period, 

 possibly the Pliocene, the bays extended further inland than they do at present. What 

 appears to be an ancient line of cliffs passes inland from the sides of Porth Nigel, by 

 Llanengan and Llangian, towards Bottwnog, and back along the eastern side of Mynydd- 

 y-Rhiw (fig. 10). The base of the old cliff is hidden under Drift, but its course 

 follows roughly the 100 feet contour line. The Drift deposits which fill much of this 

 ancient bay are now being rapidly eroded again. The Drift is rather higher on the 

 coast at Porth Nigel than it is for some way iidand, and so the drainage has been 

 altered. The Afon Soch, which appears to have a natural outlet in this bay, is deflected 

 so as to reach the sea at Abersoch (see Map). The course of an ancient pre-glacial 

 coast-line can be traced again in the region east of Llanbedrog. 



At the time of the retreat of the ice-sheet glacial lakes must have been formed in Lleyn, 

 and there are indications of overflow channels at many places, as at Trevor, in Nant Bodlas 

 near Nanhorn, and along the valley of the Soch between Llangian and Abersoch. Some 

 subsidence must have taken place during Glacial times, but there is no evidence to show 

 that the land stood at a lower level relatively to the sea than it does at present. After 

 the passing away of glacial conditions the land area appears to have had a greater extent 

 than it does now. Peat, with the roots of trees in situ, are occasionally exposed at 

 low tides in Cardigan Bay. The most recent movement would therefore appear to be 

 one of subsidence, and this view is supported by Welsh traditions regarding the loss of 

 a land area known as Cantref Givaelod which formerly extended over much of what 

 is now Cardigan Bay. 



Some geologists hold that from the onset of the land-ice to the time of its final 

 disappearance there was a period of continuous glaciation, during which the former sea- 

 basins were never emptied of their ice-sheets. This view has recently been strongly 

 advocated by Mr Lamplugh. To account for the accumulation of the stratified deposits 

 associated with the boulder clays in the West British area, somewhat extensive oscilla- 

 tions of the mer de glace are admitted. Speaking of the Isle of Man in his Presidential 

 Address to the Geological Section of the British Association (1906), he says that at the 

 time of its maximum glaciation the surface of this ice-sheet stood more than 2000 feet 

 higher than present sea-level. " Then followed a declining stage in glaciation, during 

 which the ice-sheet shrank away from the hills, which were never again covered. . . . 

 The recession of its margin was relatively accelerated in the northern part of the island, 

 so that a broad hollow was formed there between the hills and the ice-border : in this 

 hollow a mass of stratified drift was deposited." This stratified material he regards as 

 marginal " overwash " from the ice-front. Though waning and shrinking for a time, he 

 thinks the ice-sheet did not disappear entirely from the surrounding basin. " Following 

 closely upon this local deposition of stratified drift, there appears to have been a limited 

 re-advance of the ice, which brought about the accumulation of an upper boulder clay 

 on parts of the low ground." He thus admits a declining stage of glaciation. which was 

 followed after the deposition of the stratified material in a re-advance of the ice, but 



