THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 431 



of slate-rubbish heaped up along the margins of the lakes have helped to mar the 

 beauty of the scene, and in places have quite obliterated the original form of the shore- 

 line. Smaller quarries are also worked opposite the middle of Llyn Padarn on the 

 western side. Owing to the fact that the lakes are used as receptacles for the slate- 

 rubbish, quantities of this material must cover a considerable area of the lake bottom. 

 The sounding operations were at times rendered difficult, owing to the danger of 

 approaching near to these rubbish-heaps, for loose slabs and blocks continually roll over 

 and come tumbling down into the water. 



The survey of these lakes was carried out on August 14th, 15th, 1 6th, and 17th, 

 1900. The weather was favourable, and we were able to steer straight courses without 

 much difficulty. The rowing was done by a boatman from Llanberis, who proved 

 intelligent, and readily adapted himself to the work. All the soundings were taken by 

 myself. 



5. Llyn Peris. — This is the upper and smaller of the two lakes. It has an area of 

 about 598,720 square yards, and as its total length is 1930 yards, its average breadth 

 is 310 yards. 



The lake terminates somewhat abruptly at both ends, the head having a square-cut 

 form, and the lower end being a little more rounded. The outline of the lake-margin 

 is rather irregular, rocky promontories jutting out into the water here and there on 

 both sides. 



Two well-marked bays occur, one on the left side, about the middle of the lake, and 

 the other on the opposite side, but a little higher up. The lake is widest opposite to 

 the bays, the maximum breadth being 500 yards across the middle of the lake. The 

 slope of the ground is generally steep along both margins ; but the 400 contour-line 

 retreats for some distance opposite the bay on the left side, and on the right side 

 near the head of the lake, and again a little above its lower end. 



The only streams of any importance flowing into the lake are Afon IN ant Peris at 

 the head, and Afon Llwch at the lower end. The outline of the shore below the slate 

 quarries is now quite hidden by the rubbish thrown down from above, and mounds of 

 this material project well into the lake. It was impossible to take sections across 

 Llyn Peris in this region, and so long oblique sections had to be taken from points low 

 down to points high up the lake on the opposite side. The total number of soundings 

 taken in Llyn Peris was 246. The volume deduced from the soundings was 344 

 million cubic feet. The greatest depth recorded was 114 feet, and this was reached at 

 two places not far from the lower end of the lake. The mean depth is calculated to be 

 63'9 feet, being 56 per cent, of the maximum depth. The 100 feet subaqueous 

 contour-line encloses two distinct areas, one lving along the middle of the lake, and 

 the other not far above its lower termination. These two areas taper towards each other, 

 and it is quite possible that they were originally continuous, and have now become 

 separated, owing to the slipping of slate-rubbish into the middle of the lake, which is 

 constantly occurring. All the other subaqueous contour-lines are continuous. A 



