42 DR T. J. JEHU ON 



there is an exposure showing 8 to 9 feet of coarsely bedded gravelly material which 

 becomes finer when traced downwards. Amongst the pebbles were found specimens of the 

 reddish-streaked rhyolite and one of a reddish granite which is foreign to North Wales. 

 At Tan-y-llyn, near Glasfryn, there is a shaft for water, 30 feet deep, giving a 

 good section. The materia] exposed consists entirely of tough, dark greyish-blue 

 Boulder Clay full of boulders of all sizes, most of which are beautifully glaciated. The 

 clay weathers to a brownish-yellow colour just at the surface. This was the deepest 

 section met with in this region. Amongst the boulders the reddish-streaked rhyolite 

 was common. 



Another shaft for water was dug at Tyddyn- Ucha about a quarter of a mile east of 

 Tan-y-llyn. The depth reached here was 9 feet, and the material traversed consisted 

 again entirely of stiff bluish-grey Boulder Clay full of well-glaciated stones. 



At Ty-Cam, a quarter of a mile distant from Four Crosses, in the direction of 

 Pwllheli, a pit was dug for a water-wheel. Stiff bluish-grey Boulder Clay was exposed 

 to a depth of 6 feet. Below the Boulder Clay shaly rock in situ was reached. The 

 rock was much shattered just under the clay. Numerous boulders of the reddish- 

 streaked rhyolite were picked out of the deposit. 



Near Llanor, 1\ miles inland from Pwllheli, and about 5 miles from Carnarvon 

 Bay, there are brick- works in which the stiff bluish-grey Boulder Clay is exposed for 

 a depth of about 20 feet. The bottom of the deposit is not reached in the section. The 

 stiff clay is capped by 2 or 3 feet of yellowish weathered rubbly clay. Well-glaciated 

 stones were common in the lower shift clay. The boulders consist chiefly of diabase, 

 slate, etc., all of which appeared to be of Welsh origin. There were some indications 

 of shells in an extremely fragmentary condition. The reddish-streaked rhyolite was 

 seen imbedded in the clay. 



Passing west of a line from Pwllheli to Nevin the low grounds are underlaid by 

 Boulder Clay and the smaller hills are covered by gravels and sands. Exposures are 

 not common, but a few may be mentioned. On the hill immediately to the south of 

 Tu-hivnt-i'r-afon Inn, Rhyd-y-clafdy, sand and gravel are exposed in many shallow- 

 pits. Near the surface the material is gravelly, with a somewhat clayey matrix, and 

 below this we find fine yellow marine-like sand. The exposures are only 4 to 5 feet 

 deep, but the sands must attain a considerable thickness towards the base of the hill. 

 Several gravel pits are found between Bodvean and Cors Geirch. One of these lies 

 a quarter of a mile west of Bodvean, and shows a section 1 5 feet deep. It is situated 

 on the slope of a hill at a height of almost 200 feet above sea-level. The deposits seen 

 are mostly sands, fine, yellow in colour, and marine-like. Some pebbly layers occur, 

 and at the top a little yellowish clay passing into soil. A little further south is found 

 another with an exposure 6 to 7 feet deep. This is at a height of 175 feet above sea- 

 level. It consists mostly of gravelly material getting finer and more sandy below. 

 On the same hill slope, but at lower levels, fine yellow marine-like sands are exposed 

 at several places. The entire hill is evidently covered by a mantle of gravel and sand. 





