240 BATHYMETKICAL SURVEY OF 



On July 14, 1903, the surface-level was 52-9 feet above the sea, almost 

 identical with the elevation determined by the Ordnance Survey officers on 

 August 24, 1900, viz. 53'0 feet. The basin is simple, the bottom sloping 

 on all sides to the deepest water, a little north of the middle line. The 

 variation of temperature from surface to bottom was only ^ : 



Surface 54-8 Fahr. 



25 feet 54-6 



70 . 54-3 



Grass Water (see Plate CI.) is a narrow loch, to the west of Houllma 

 Water in Aithsting. It lies amid low moorland, and measures two-thirds 

 of a mile in length from north to south. The centre line of the loch 

 is strongly curved. The greatest breadth, one-sixth of a mile, is at 

 the north end, which is very shallow and obstructed by numerous 

 boulders. At this end there are several small islands. The narrow 

 southern portion is slightly deeper, with the maximum depth of 6 feet. 

 The whole loch is filled with vegetable growth. The superficial area is 

 34 acres, and the contents 4 millions of cubic feet. The Yoxna burn, 

 a considerable stream, conveying the overflow of Houllma Water and of 

 several smaller lochs, enters at the southern extremity, and four or five 

 smaller burns on the west shore. The outflowing stream passes north- 

 ward through the little Loch Culeryn into the Vadills, at the head of 

 Uni firth. The drainage area, including several fairly large lochs 

 not surveyed, measures 3 square miles. The height of the loch above 

 sea-level was not ascertained, but it may be estimated from a spot-level 

 of 11 feet on the shore to be about 10 feet. 



The surface temperature on July 15, 1903, was 58'0 Fahr. 



Upper Loch of Brouster (see Plate 01.) is a small loch about 5 miles 

 south-east from Sandness. It is of oblong form, with the axis running 

 north and south. It is the lowest of an extensive chain of lochs, stretch- 

 ing right across the peninsula, from near Sandness to the Browland Voe 

 near Walls. The chain includes several fairly large lochs, of which only 

 Burga Water was surveyed, there being no boat on the much larger 

 Voxterby Loch. The loch is fully one-third of a mile long, one-eighth 

 of a mile broad, with an uneven bottom, varying from 5 feet to 8 feet in 

 the centre, and a very small part 11 feet deep near the south end. The 

 mean depth is 5J feet, the area about 22 acres, and the volume 5 millions 

 of cubic feet. 



The area draining into the loch is 5J square miles. The Brace burn, 

 from Voxterby Loch, comes in at the north end. A short stream flows 

 south into the Loch of Brouster, a sea loch, and a branch of the Brow- 

 land Voe. The level of the loch was not found, but it was stated that the 

 water might fall a little lower, and might rise 5 to 6 feet higher than on 

 the date of the survey (July 20, 1903). The surface temperature was 

 54-2 Fahr. 



