THE FRESH- WATER LOCHS OF SCOTLAND. 
243 
whicli is nearly flat-bottomed, but slightly deeper towards the east side, the 
greatest depth is 12 feet. In the southern basin the maximum depth of 13 
feet is close to Quoy ness, and it gradually shoals to the south end of the 
loch. This basin is constricted in the middle by the Castle Holm and a 
number of other islands. In superficial area, which is 331 acres, or about 
half a square mile, the Loch of Strom is the largest, as it is also the 
longest, in Shetland. The low mean depth, 7 feet, gives a relatively small 
volume of only 101 millions of cubic feet, which is equalled by one loch 
(Clings Water), and exceeded by four lochs (Eela, Cliff, Spiggie, and 
Girlsta). 
The Loch of Strom has an extensive drainage area, including Sand 
Water, and the whole central valley of the Mainland for almost 6 miles 
north, or almost as far as Voe. The upper part of this valley, where 
the stream flows south from Petta Water, is known as Tetta vale; after 
passing through Sand Water it becomes Sand water burn, and flows into 
the north end of the Loch of Strom, under the name of Strom Firth burn. 
The drainage area extends to nearly 8 square miles, or about half a square 
mile less than that of the Loch of Cliff. The surface temperature varied 
from 56°-8 to 57°*2 Fahr. in different parts of the loch. 
Loch of Tingwall (see Plate CHI.) is a fairly large loch of oblong 
form, 4 miles west of Lerwick, and 2 miles north of Scalloway. It 
occupies, with the Loch of Asta, a narrow valley running across the 
Mainland, nearly from north to south, between Tax firth and Cliff sound. 
The whole west side of the loch is cultivated, with high hills rising 
behind; on the east is moorland, with sparse heather. At the north 
end is a flat strip of meadow, liable to floods. On the western shore 
are a few large boulders and bosses of rock. The island in the centre is 
low and covered with heather. The length is just over a mile, and the 
greatest breadth nearly a quarter of a mile. 
The loch is divided into two nearly equal portions by a constriction, 
where it is also very shallow, the depth in the centre of the narrows being 
only 9 feet. It is still shallower in the channels on either side of the 
island north of the narrows, where the depths are only 2 and 3 feet. The 
northern basin is the shallower. It is almost flat-bottomed over the 
greater part of the area, with depths of from 7 to 9 feet. In the centre is 
a very small and abrupt depression, in which there is a depth of 40 feet. 
The southern basin is of a difterent character ; as shown by the contours, 
the sides slope fairly regularly to the centre, where there is the maximum 
depth of 60 feet. The mean depth is about 19 feet, the area nearly 107 
acres, and the volume of water 87 millions of cubic feet. No large streams 
enter the loch ; its outflow is to the south, by a stream about 100 yards 
long, into the Loch of Asta. There is rock close to the outflow, on the 
west side, and the burn flows among stones, with rock in the channel a 
few yards from the loch. 
