THE FRESH-WATER LOCHS OF SCOTLAND. 15 



where the deposit is white and calcareous, and it was a regular practice 

 some few years ago to dredge the loch to the south of the island, and 

 to use the mud for marling the land. 



Loch Watten (see Plate III.). Loch Watten, the largest of the Caith- 

 ness lochs, is situated about midway between Wick and Thurso, the 

 railway between those places running along its northern shore, and the 

 main road skirting its southern shore. The loch trends in a north-west 

 and south-east direction, with a slight sinuosity in the outline, the upper 

 portion being narrower than the main body of the loch, and bending in a 

 northerly direction. It is 3 miles in length, with a maximum breadth 

 towards the lower end of three-quarters of a mile, the mean breadth being 

 about half a mile. Its waters cover an area of about 930 acres, or about 

 H square miles, and it drains directly an area of over 13 square miles, but 

 since it receives the overflow from Loch Scarmclate its total drainage area 

 is about 20J square miles. The maximum depth observed was 12 feet, 

 and no fewer than thirty-six soundings were taken at this depth in the 

 south-eastern half of the loch. The volume of water is estimated at 341 

 million cubic feet, and the mean depth at 8J feet. The loch was surveyed 

 on October 8 and y, 1902, when the elevation of the lake-surface was 

 found to be 54*9 feet above the sea ; when levelled by the officers of the 

 Ordnance Survey on December 28, 1869, the elevation was 55'4 feet above 

 sea-level. According to the miller at Watten, the wind sometimes per- 

 ceptibly affected the level of the water, and after an easterly wind had 

 been blowing strongly for some time it was impossible for him to work 

 the mill, the water being driven before the wind and piled up at the 

 north-west end. The water might rise 2 feet above, and fall 1 foot 

 below, the level on the date of the survey. 



Loch Watten may be described as a large, shallow, flat-bottomed 

 basin, the deeper portion lying towards the south-eastern end, the water 

 shoaling more gradually on proceeding towards the north-western end. 

 The great majority of the soundings were taken in depths exceeding 

 5 feet, and more than one half of the lake-floor is covered by more than 

 10 feet of water. The mean depth of the entire basin is 70 per cent, of 

 the maximum depth. The temperature of the surface water at 10 a.m. on 

 October 8, 1902, was 49'9 Fahr., and at 10 a.m. on October 9, the surface 

 temperature was 49 0< 6, while a reading at 12 feet gave 49'o. 



Loch Hempriggs (see Plate III.). Loch Hempriggs lies about 2 miles 

 to the south-west of the town of Wick, and within a mile of the shores of 

 the North Sea, though the outflowing stream pursues a long and devious 

 course in a northerly direction before joining the Wick water on its way 

 to the sea. The loch is irregularly subcircular in outline, and the 

 maximum diameter from north to south and from east to west is in 

 each case about three-quarters of a mile. The superficial area is about 



