44 DR T. J. JEHU ON 



Going westwards, at Plas-ym-mhenllech a sand pit was found in a field near the 

 junction of the roads to Sarn and to Aberdaron. There were exposed here 5 feet of 

 coarse sand in which were seen streaks of stiff clay. 



Going south again similar deposits are found at the surface in the neighbourhood of 

 Sarn and Bottwnog. Near Llangian, just where the road turns off to Llawr-y-dref, 

 there is a gravel pit in which 10 feet of coarse gravel are exposed. The gravels show 

 faint indications of bedding. Another gravel pit is seen at Neigivl-Plas, in front of the 

 house, the gravel being coarse and disclosed to a depth of 4 or 5 feet. All about the 

 farm are many other disused pits of a similar nature. The gravels often pass down- 

 wards into fine sands. A pit at Neigwl Ganol shows stony yellow weathered clay at 

 the surface and to a depth of 4 feet. In a gravel pit at Talsarn the material is more 

 rubbly — the stones being less rounded and more flaky. Above Talsarn Bridge the Afon 

 Horon is seen to run on the stiff bluish-grey Lower Boulder Clay. This can be traced 

 right up the stream, which further up its course becomes a mere rill and does not appear 

 anywhere to reach the solid rock. 



The area between Abersoch and Porth Nigel is largely covered with sands. These 

 are well exposed near Cim, at a height of over 200 feet above sea-level. The sands are 

 fine and marine-like and have a yellow colour. 



Rhos-hirivawn, south-west of Llangwnadl, seems to be underlain by a stony 

 weathered Boulder Clay. As we approach the extremity of Lleyn the mantle of Drift 

 tends to become thinner until a mere skin of yellow weathered stony clay is left. 



No systematic examination was made of the erratics lying on the surface of the land, 

 but in traversing the inland region in search of sections of the Drift the following were 

 noted : — 



On Y Foel, between Llanllyfni and Clynnog Fawr, a block of felsite lies perched on 

 the slate at a height of over 600 feet above the sea-level. 



On Y Gym Goch, at a height of 8()0 feet, a small boulder of the Eskdale granite 

 was found, and a little lower down another of a granite from the south-west of 

 Scotland. 



East of Porth Nant, on the western slope of Yr Eijl, a boulder of Carboniferous 

 Limestone was picked up at a height of 450 feet. 



Near Tan-y-foel, between Llithfaen and Pistyll, a boulder of greyish-white granite, 

 probably Scottish, was obtained at an elevation of over 500 feet. 



At the gate leading to Berth daur-fawr, near Penllech, there stands a huge boulder 

 measuring 5 feet by 3 feet by 1^- feet. It is a very fresh-looking basic rock. A 

 fragment was taken away and subsequently sliced and examined under the microscope. 

 It proved to be a beautifully fresh olivine dolerite showing typical ophitic structure. 

 Jt is difficult to locate its place of origin. The large size of the boulder makes one 

 doubt whether it can have come from the west of Scotland, where similar rocks are found. 

 It may possibly have been derived from some Tertiary dyke in Anglesey. 



On Penllech were found erratics consisting of granites, a quartz-porphyry with the 



