THE LAKES OF SNOWDONIA AND EASTERN CARNARVONSHIRE. 445 



able in that no streams of an) 7 importance run into it. Several tiny streamlets are 

 marked on the map as flowing in from the left side, and the largest of these occurs near 

 the lower end. Those marked as entering; the head of the lake are the merest rills. The 

 right side is almost altogether free from water-courses. But after heavy rains, no doubt 

 water comes flowing down the mountain slopes, especially on the left side. From the 

 foot of the lake escapes the Afon Ddu, which pursues its way north-eastwards through 

 a gently sloping valley largely covered with drift. 



The surface of Llyn Cawlyd is, according to the Ordnance Survey map (April 

 1887), 1L64'G feet above sea-level. It has a total length of 2855 yards, with a 

 maximum width of 495 yards. The mean breadth is 335 yards, being 12 per cent, of 

 the length. Its waters cover an area of about 957,800 square yards. The lake was 

 surveyed on 25th June 1901, under the most favourable weather conditions. All 

 the soundings were taken by mvself, and the rowing was done by an excellent boatman. 

 During the work on this lake, I was accompanied by Mr H. Woods, M.A., St John's 

 College, Cambridge. The total number of soundings taken was 99. The greatest 

 depth observed was 222 feet. The volume of water contained in the lake is estimated 

 to be approximately 941 million cubic feet, and the mean depth at 109*1 feet, or 49 

 per cent, of the maximum depth. An examination of the map (Plate VII.) will show 

 that the configuration of the floor of the lake is extremely regular and simple. The 

 deepest area is approximately in the centre of the lake, and has the form of a long 

 narrow depression, with depths exceeding 200 feet. Within this a still narrower 

 depression, with depths over 220 feet, is marked on the map. The 200 feet depression 

 has a maximum width of about 180 yards, aud a length of a little over 1000 yards, and 

 it has an area corresponding to nearly 16 per cent, of the total superficial area of the lake. 



The 100 feet depression is over 2000 yards in length, with a maximum breadth of 

 about 340 yards. The area enclosed between the 100 feet and 200 feet contour-lines is 

 356 per cent, of the entire area of the lake ; this, added to the area lying within the 200 

 feet contour-line, gives over 50 per cent, of the total area for depths of over 100 feet. 



The 40 feet depression is 2400 yards in length, with a maximum width of about 

 430 yards; the area enclosed between the 40 feet and 100 feet contour-lines is about 

 25 per cent, of the total area, and this added to the area lying within the 100 feet sub- 

 aqueous line, gives over 75 per cent, of the entire area of the lake for depths of over 

 40 feet. The area lying between the 20 feet contour-line and the coast corresponds to 

 only 23 '9 per cent, of the entire area. 



There is a comparatively shallow area near the foot of the lake, and the soundings 

 gave indications of a subaqueous ridge rising from the lake bottom not far from the 

 lower end. 



Most of the contour lines follow pretty closely the outline of the lake, and so the 

 form of the floor is very simple, It is a steep and narrow trough. Along the axis 

 it deepens rapidly at first, and then more slowly to 200 feet a little more than a half 

 •of a mile from the head, maintains this depth for more than half a mile further, the ramp 



