464 



A. L. Leach — Glacial Drift and Raked Beach 



identical with that described by me, but Prestwich drew no distinction 

 between the head and the glacial drift. 



About a quarter of a mile south-west of the little harbour of 

 Forth Clais, near St. Davids, a mass of glacial drift forms a well- 

 marked terrace, roughly semicircular in outline and convex towards 

 the sea. In the low cliff or steep bank on the seaward margin of this 

 terrace, which overlooks an inlet named on the 6 inch map Ogof golchfa, 

 the glacial drift is seen resting in part on the solid rock and in part 

 overlapping upon the raised beach (see Figure). From the western end 

 a level rock-platform, about 15 feet above high-tide level, extends 

 almost horizontally for about 50 yards across Lower Cambrian shales 

 and sandstones,- and then, rising slightly, passes over an igneous 

 dyke (only a few feet wide) which has heen planed down almost 

 to the general level of the platform. A few yards further to the 

 east a huge dyke fully 40 feet wide intersects the Cambrian shales, 

 and the cleanly cut platform ends. Upon the platform rest many 

 large well-worn boulders (closely resembling the beautifully ovoid 

 boulders of the raised beach at Whitesand Bay, St. Davids) embedded 



Diagram section of the Raised Beach and Boulder-clay near Port Clais, 

 St. Davids. g, glacial deposit (Boulder-clay) ; h, head ; s, stratified 

 shingle and boulders of the raised beach ; a, b, striated boulders of the 

 raised beach ; c, striated rock-surface. 



in concreted beach shingle composed largely of flatfish ovoid pebbles 

 of various igneous rocks. The shingle, which is about 10 feet 

 thick at its western end, contains many partly worn blocks of 

 Cambrian shale and pebbles of sandstone, but igneous pebbles 

 predominate, especially in its lower part, and the whole deposit, 

 except the non-local boulders and pebbles, appeal's to be an old 

 pebble beach such as might accumulate about high-tide level at 

 the foot of cliffs composed of shales and sandstones with igneous 

 intrusions. Upon the shingle lies head a few feet thick composed of 

 angular debris from the rocks above. These two deposits are 

 referable to the shingle and head of the Gower Raised Beach Series : 

 the intermediate blown sand of Gower is not here represented. Over 

 the head, and to some extent cutting into and mingling with it, 

 lies a drift deposit (containing boulders), which 1 consider to be 

 glacial and separable from the head, and to be directly continuous 

 with Boulder-clay which some yards further east ploughs quite 

 through the raised beach deposits and comes to rest on the solid 

 rock. Although the western end of the section is inaccessible, it 



