THE FRESH-WATER LOCHS OF SCOTLAND. 



371 



to 100 feet 

 100,, 200 

 200,, 300 

 300 400 

 Over 400 , 



415 acres 

 294 

 440 

 256 

 135 



1540 , 



27 '0 per cent. 

 19-1 ' 



28-6 



16-6 



8-7 



100-0 



The striking characteristic brought out by this table is the 

 large area of the lake-floor covered by water between 200 and 300 

 feet in depth an area greater than in either of the two shallower 

 zones. 



Temperature Observations. At the early season when Loch Treig 

 was surveyed, the surface was very little warmer than the bottom, the 

 whole difference between the surface and 300 feet, on May 29, when the 

 last series was taken being only l-7 Fahr. Five days earlier, May 24, 

 the difference was only 0< 7. In the interval the surface had risen 

 in temperature l-6, while at 300 feet the rise was only 0-6. The three 

 serials are contrasted in the table appended : 



AnDubh Loclian (see Plate LXXXIX.). A very small loch situated 

 about halfway between Loch Treig and the river Spean and a little to 

 the west of the river Treig. It lies at an elevation of 785 to 790 feet 

 above the sea, at the west side of an extensive deposit of gravel and 

 sand, hills of moderate height rising on the west shore (see Fig. 57). 

 It is of somewhat oblong form, diversified by many little bays, and is 

 shallow and weedy towards the south end. It is nearly a quarter of a 

 mile long, and covers an area of about 8i acres. The greatest depth is 

 40 feet, and the mean depth 15J feet. The volume of water amounts 

 to 6 millions of cubic feet. It has a drainage area of about one-sixth 

 of a square mile, receiving only local superficial water. It drains by 

 a small stream northward into the river Spean. 



