24 DR T. J. JEHTJ ON 



The general succession of the Drift deposits in this bay is therefore as follows : — 



5. Soil. 



4. Yellowish-brown weathered rubbly clay often becoming pebbly or passing into a 



mass of boulders. 

 3. Stoneless laminated silty clay. 

 2. Sands and Gravels. 

 1. Lower Boulder Clay. 



The silty clay (3) shows fine laminations which are arranged in ribands of lighter 

 and darker colours, giving a striped or banded appearance as seen from the shore. The 

 bands are sometimes wavy, and examples of faulting occur as described by Mr Mellard 

 Reade, # and ascribed by him to contraction and loss of volume, either by actual drying 

 or by the draining away of their water. 



At the north-east end of the bay the upper part of the cliff consists of Rubble Drift. 

 The lower part is grassed over, but appears to be sandy and gravelly. 



Penrhyn Nevin, the promontory separating this bay from Porth-dinlleyn, has rock at 

 the base and Drift deposits above. Ice-scratches running N.N.E. to S.S.W. are seen on 

 the rocky platform. This platform runs at a height of 1 to 1 2 feet above the modern 

 beach, and is now much cut into, being in process of demolition by the waves. In 

 appearance it simulates an old shore platform. It is often clear of drift for 7 to 8 yards 

 from its seaward margin, and has a gentle slope outwards. Portions of it can be traced 

 on both sides of the promontory as well as round its point. Where the rock-shelf passes 

 under the cliff of Drift it has often a hummocky and glaciated aspect, in striking contrast 

 to the rough and jagged appearance shown by the rocks on the shore below. On the 

 Nevin side of the promontory the Sands and Gravels are, as already mentioned, sometimes 

 separated from the platform by a foot or so of rock rubble. On the Porth-dinlleyn side 

 clays, somewhat laminated, rest on the rock and are followed above by sand and gravel. 



Porth-dinlleyn lies to the south-west of Porth Nevin. This bay is wider than that 

 at Nevin, having an extent of about 2 miles. Its western horn is formed by a mass 

 of coarse serpentinous rock. The cliff has a very uniform height of about 100 feet. 

 Its face is much grassed over, so that good sections are not often displayed. The deposits 

 are very similar to those met with in Porth Nevin. They consist largely of stoneless 

 sands and gravels capped by the Upper Stony Clay. At the north-east end of the bay 

 stoneless, stiffish laminated clays form the lower part of the cliff. Nearer the middle of 

 the bay these are seen to pass downwards into the typical tough Lower Boulder Clay. 

 At a point just east of the middle a ledge of rock appears from under the Drift. The 

 surface of this has a glaciated appearance. Beyond the ledge the Lower Boulder Clay 

 appears at the base of the cliff with big boulders imbedded in its upper part. A little 

 further west, beds of gravel come down to the bottom of the cliff face, and are followed 

 above by stoneless sands. The upper portion of the cliff is here hidden by overgrowth. 



* Geol. Mag., 1891, p. 487. 



