240 
BATHYMETRICAL SURVEY OF 
On July IT, 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 slojung 
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 61°-8 Fahr, 
25 feet 54°-6 „ 
70 „ 54°-3 „ 
Grass Water (see Plate Cl.) 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. 
Up'per Loch of Brouster (see Plate CL) 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 54 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. 
