THE FRESH-WATER LOCHS OF SCOTLAND. 
345 
and the difference in level only IJ feet. The term Gedd Lochs is 
applied to the connected series, consisting of Loch an Gead, Loch an 
Tachdaidh, and the neighbouring little Loch an Gobhlach, which was 
not sounded. Loch an Tachdaidh is irregular in outline, trends in a 
north-east and south-westerly direction, and is nearly two-thirds of a 
mile in length, with a maximum breadth exceeding one-third of a mile. 
Its waters cover an area of about 92 acres, and it drains directly an 
area exceeding 4 square miles, but since it receives the overflow from 
Loch Calavie, its total drainage area is over square miles. The 
maximum depth of 62 feet was observed in the centre of the north- 
eastern portion of the loch, near a heap of stones showing above the 
surface of the water. The volume of water is estimated at 72 million 
cubic feet, and the mean depth at 18 feet. The loch was surveyed on 
October 21, 1904; the elevation could not be determined by levelling, 
but was estimated at about 831 -5 feet above the sea. 
Loch an Tachdaidh is irregular in conformation as well as in out- 
line, and, besides the island of stones already mentioned, includes four 
small unnamed islands, the largest of which occupies a central position ; 
the south-western portion is shallow and filled with weeds. The 
contour-lines are sinuous in character, the deepest part lying between 
the largest island and the heap of stones, where three soundings ex- 
ceeding 50 feet in depth were taken. To the south of the largest 
island, and towards the eastern shore, a sounding in 25 feet was 
recorded, surrounded by shallower water. The area of the lake-floor 
covered by less than 25 feet of water is about 74 acres, or 81 per cent, 
of the total area. 
Temperature Observations . — The following series of temperatures 
taken in the position of the deepest sounding shows a range of only 
1°*2 Fahr. throughout the body of water, the deeper layers being 
uniform in temperature : — 
Surface 46'’ *2 Fahr. 
.30 feet 45° -0 „ 
60 „ 45° -0 „ 
An Gead Loch (see Plate LXXXII.). — An Gead Loch lies to the 
north-east of Loch an Tachdaidh, and trends in a similar direction, but 
is more regular in outline and more uniform in width. An Gead Loch 
is nearly miles in length, with a maximum width towards the south- 
west end of a quarter of a mile. The superficial area is about 110 acres, 
and the area draining directly into it is about 2J square miles, but 
since it receives the outflow from Lochs Calavie and an Tachdaidh, 
the total drainage area exceeds 9 square miles. The maximum depth of 
30 feet was observed towards the north-eastern end of the loch. The 
volume of water is estimated at 54 million cubic feet, and the mean 
depth at llj feet. The loch was surveyed on October 21, 1904, and the 
