252 BATHYMETRICAL SURVEY OF 



Portmore Loch (see Plate CIX.) lies a little more than 2 miles to the 

 south-west of Gladhouse reservoir, and is two-thirds of a mile in length 

 from north to south, with a maximum breadth of one-third, and a mean 

 breadth of a quarter, of a mile. The superficial area is about 105 acres, 

 and the drainage area exceeds 3 square miles. It is a simple, flat-bottomed 

 basin, the 10-feet contour closely hugging the shore all round, and the 

 20-feet contour enclosing an area in the northern harlf equal to one-fourth 

 of the total area, the maximum depth of 41 feet being recorded about a 

 quarter of a mile from the north end. The area covered by less than 

 10 feet of water is one-fifth of the total area, so that about 55 per cent, 

 of the lake-floor is covered by water between 10 and 20 feet in depth. 

 The volume of water is estimated at 76 million cubic feet, and the mean 

 depth at nearly 17 feet. When surveyed on July 4, 1903, the elevation 

 could not be determined; on December 23, 1892, the Ordnance Survey 

 officers found it to be 999*0 feet above sea-level. The temperature of the 

 water was practically uniform throughout, the readings at the surface and 

 at 20 feet being identical, viz. 57'5 Fahr., while a reading at 40 feet 

 gave 57'l. 



Edgelaw Reservoir (see Plate CVIII.) lies about 5 miles to the north- 

 east of Portmore Loch, and little more than half a mile to the north-west 

 of Rosebery reservoir. It is elongated and irregular in outline, with 

 curved axis, trending generally in a west-to-east direction, and is two-thirds 

 of a mile in length by only one-sixth of a mile in maximum breadth. The 

 superficial area is only 35 acres, while the drainage area, including Port- 

 more Loch, exceeds 10 square miles. Though one of the smallest of the 

 Forth reservoirs, it is the deepest, having a maximum depth near the 

 outflow of 77 feet, while the mean depth is over 31 feet, the volume of 

 water being estimated at 47 million cubic feet. The bottom is uneven, a 

 small 50-feet basin occupying a central position, and being separated by 

 shallower water from the main 50-feet basin at the east end, where deep 

 water approaches very close to the shore. 



When surveyed on July 7, 1903, the elevation was 650'9 feet above 

 the sea. Temperatures in the deepest part showed a range of ll-4 Fahr. 

 from surface to bottom, but no very rapid fall of temperature is indicated 

 by the readings : 



Surface 60-0 Fahr. 



15 feet 57'3 



30 52-6 



70 48-6 



Duddingston and St. Margaret's Lochs (see Plate CX.). These two 

 small shallow lochs, situated at the base of Arthur's seat in the immediate 

 neighbourhood of Edinburgh, were sounded. Duddingston covers an area 

 of about 20 acres and St. Margaret's about 4 acres, the maximum depths 



