THE FRESH- WATER LOCHS OF SCOTLAND. 345 



and the difference in level only 1^ 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 6J 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 8.1 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 1J 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 11 J feet. The loch was surveyed on October 21, 1904, and the 



