252 
BATHYMETKICAL 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 half 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. YVhen 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°*1 . 
Edgelaio Peservoir (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 Eosebery 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, w’hile 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 11°*4 Fahr. 
from surface to bottom, but no very rapid fall of temperature is indicated 
by the readings 
Surface ... 
15 feet ... 
30 ,, ... 
70 „ ... 
60°'0 Fahr. 
57°*3 „ 
52°-6 „ 
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 
