THE FRESH-WATER LOCHS OF SCOTLAND. 253 



being respectively 10 and 5 feet, the mean depth in each case being one- 

 half of the maximum. The volume of water in Duddingston is about 

 4 million cubic feet, and in St. Margaret's about half a million cubic feet. 

 They were surveyed on June 27, 1903, when the temperature of the water 

 in Duddingston was 61'l Fahr., and in St. Margaret's 60'7. 



Harper rig Reservoir (see Plate CXI.) is situated at the base of the 

 Pentland hills, about 12 miles south-west of Edinburgh. It exceeds a 

 mile in length from south-west to north-east, with a maximum breadth 

 of half a mile, the superficial area being about 226 acres. It is, on the 

 whole, comparatively shallow and flat-bottomed, with a small area of deep 

 water near the outflow, the maximum depth of 30 feet being recorded 

 close to the weir. More than one-half of the bottom is covered by water 

 between 10 and 20 feet in depth, while only 4 per cent, is covered by 

 more than 20 feet of water. The volume of water is estimated at 

 108 million cubic feet, and the mean depth at 11 feet. When surveyed 

 on July 21, 1903, the elevation was 891-9 feet above sea-level. 



ir Reservoir (see Plate CXII.) lies about 4 miles to the 

 north-east of Harperrig reservoir, and is practically continuous with 

 Harelaw reservoir, though standing about 25 feet higher. These two 

 contiguous basins form a perfect contrast in conformation, Threipmuir 

 covering an area six times greater than that of Harelaw, but being 

 relatively shallow. Indeed, the south-western portion is merely a swamp. 

 Threipmuir reservoir is 1J miles in length from south-west to north-east, 

 excluding a narrow arm branching off to the east ; from the extremity of 

 this arm to the extremity of the south-western swampy portion is fully 

 '2 miles. The superficial area is about 192 acres, while the drainage area 

 exceeds 6 square miles. The maximum depth of 17 feet occurs near the 

 outflow, whence the water shallows gradually on proceeding to the south- 

 west or along the narrow arm to the east. The volume of water is esti- 

 mated at 66 million cubic feet, and the mean depth at 8 feet. When 

 surveyed on July 1, 1903, the elevation was 831 '5 feet above the sea, and 

 the temperature of the water was uniform, the reading at the surface being 

 59-3 Fahr., and at 10 feet 59-2. 



Harelaw Reservoir (see Plate CXII.) is irregular in outline, and exceeds 

 half a mile in length from south-west to north-east, covering an area of 

 only 30 acres, and draining an area of 7 square miles, including Threip- 

 muir. The depth increases gradually on proceeding from the inflow 

 towards the outflow, where a maximum of 54 feet was recorded. The 

 volume of water is estimated at 30 million cubic feet (nearly half that 

 of Threipmuir), and the mean depth at 23 feet (nearly three times that of 

 Threipmuir). When surveyed on July 1, 1903, the elevation was 806'0 

 feet above the sea. Temperatures taken in the deepest part gave some 



