322 BATHYMETRICAL SURVEY OF 



Surface . 55'8 Fahr. 



2 feet 55-7 



3 55*4 



3-5,, 55'2 



4 53-6 



5 53'4 



10 53-0 ,, 



20 53'l ,, 



This series shows a range of 2 0> 8, there being a fall of no less than 

 l-6 between 3J and 4 feet. 



Loch an Dithreibh (see Plate LXXVL). Loch an Dithreibh (or 

 Deerie, or Derry) lies less than 3 miles to the south of the head of the 

 Kyle of Tongue, with Ben Loyal to the east and the lofty Ben Hope, a 

 magnificent object in the landscape, to the west. The general trend 

 of the loch is north-north-east and south-south-west, the main body 

 of the loch trending almost north and south, and throwing out an arm 

 towards the north-east. The loch is over l miles in length, the main 

 body being approximately uniform in width, with a maximum breadth 

 of two-thirds of a mile, while the north-eastern arm is much narrower ; 

 the mean breadth of the entire loch is nearly half a mile. Its waters 

 cover an area of about 475 acres, or three-quarters of a square mile, 

 and it drains directly an area of 10 square miles; but since it receives 

 the overflow from Loch Chaluim, its total drainage area is 12f square 

 miles. The maximum depth of 157 feet was observed approximately 

 near the centre of the main body of the loch. The volume of water 

 is estimated at 1366 million cubic feet, and the mean depth at 66 feet. 

 The loch was surveyed on October 1, 1902, when the elevation of the 

 lake-surface was found, by levelling from bench-mark, to be 267*45 

 feet above the sea ; when levelled by the officers of the Ordnance Survey 

 on October 26, 1870, the elevation was 267*8 feet above sea-level. 



Loch an Dithreibh includes two basins (1) a larger deep basin in 

 the main body of the loch, and (2) a smaller shallower basin in the 

 north-eastern arm, separated by a rise of the bottom on which the 

 deepest sounding was 49" feet. The maximum depth observed in 

 the small subsidiary basin was 59 feet, and the separating ridge is 

 irregular, for a sounding in 21 feet was taken in its central part 

 surrounded by deeper water. The 25-feet contour-line is continuous 

 from end to end of the loch, coinciding approximately with the outline 

 of the loch, but approaching close to the eastern shore off Creag an 

 Dithreibh and Creag na Luath-ghaire. The 50-feet area is cut into 

 two portions, as already indicated, the main portion approaching close 

 to the southern end of the loch and exceeding 1 mile in length. The 

 75-feet area is nearly a mile in length, and at its northern border the 

 lake-floor shows conspicuous undulations, giving to the 75-feet contour- 



