112 BATHYMETRICAL SURVEY OF 



a gradient of 1 in 4-2. The area of the lake-floor covered by less than 

 10 feet of water is about 52 acres, or 70 per cent, of the total area of 

 the loch; that covered by water between 10 and 25 feet in depth is 

 about 18 acres, or 25 per cent. ; and that covered by more than 25 feet 

 of water is about 4 acres, or 5 per cent, of the entire area of the 

 loch. Loch Long was surveyed on June 24, l)03, and its elevation 

 above the sea was determined, by levelling from bench-mark, as 724-0 

 feet. 



Temperature Observations. Temperatures taken in the deepest part 

 of the loch gave the following results : 



Surface 58'4Fahr. 



10 feet 57'0 



15 -.. ... 55-4 ,, 



20 54-0 ,, 



40 53-2 ,, 



This series shows a range of temperature throughout the 40 feet of 

 water of 5-2, there being a fall of 3 between 10 and 20 feet. 



Pitlyal Loch (see Plate XXX.). Pitlyal Loch (or Round Loch, or 

 Thriepley Loch) lies about a quarter of a mile to the south-east of Long 

 Loch, and is surrounded by gently sloping cultivated fields. There is 

 a fringe of weeds all round the shore. Grebe and coots were seen, and 

 there were swans on the small islet with bushes about 100 feet north- 

 west of the boathouse. The outflow to the Dighty burn is by artificial 

 dam and sluice; the water may rise 2 to 3 feet above its level on the 

 date of the survey. The loch is well described by its name " Round 

 Loch," for it is subcircular in outline, though rather longer from north 

 to south than from east to west. It is over one-fifth of a mile in length, 

 with a maximum breadth of about one-seventh of a mile, the mean 

 breadth being about one-ninth of a mile, or 52 per cent, of the length, 

 and its waters cover an area of about 15 acres. Thirty soundings were 

 taken, the maximum depth observed being 19 feet. The volume of 

 water is estimated at 5,347,000 cubic feet, and the mean depth at 

 8J feet, or 44 per cent, of the maximum depth. Pitlyal Loch forms a 

 simple basin, but the deeper water is found towards the western shore, 

 so that the slope of the bottom is steeper off that shore than off the 

 eastern shore; a sounding of 11 feet was taken about 100 feet from the 

 western shore, and the maximum depth of 19 feet was recorded about 

 150 feet from that shore. The area of the lake-floor covered by less 

 than 10 feet of water is nearly 10 acres, or 65 per cent, of the total 

 area of the loch. Pitlyal Loch was surveyed on the same day as Long 

 Loch (June 24, 1903), and its elevation above the sea was determined 

 by levelling from bench-mark as being 606-5 feet. 



