366 BATHYMETRICAL SURVEY OF 



portions ; the largest of these approaches the west end of the loch, and 

 is 2J miles in length. Two lesser areas, each about two-thirds of a mile 

 in length, occur close together in the narrow middle part of the loch. 

 The 75-feet area towards the upper end of the loch is nearly 1 J miles in 

 length. The shallowings between these various basins are all opposite 

 the mouths of streams, but in one instance the stream is too small to 

 account for the shallowing, and other larger streams appear to have had 

 no effect on the contours. The largest 75-feet basin includes two areas 

 of over 100 feet, a very limited one in the narrow part of the loch, with 

 a maximum depth of 105 feet, and another, 1 J miles in length, near the 

 west end. This 100-feet area is at the broadest and deepest part of the 

 lake, and includes an area, two-thirds of a mile in length, of over 150 

 feet, in which two soundings of 174 feet and 170 feet respectively were 

 taken, with a shallowing of 155 feet between them. The two small 

 75-feet areas near the middle of the lake include depths of 112 and 114 

 feet respectively. The easternmost 75-feet area includes two very small 

 basins of over 125 feet, with maxima of 133 and 141 feet. Many lesser 

 irregularities occur. For about half a mile from the inflow of the 

 river Pattack the loch is very shallow, and the bottom and shores 

 are sandy. 



The approximate areas between the contour-lines at intervals of 

 50 feet, with the percentages to the total area of the loch, are given 

 in the following table : 



to 50 feet 765 acres 40 '3 per cent. 



50 100 ,, 686 ,, 36-1 



100., 150 396 ,, 20-8 



Over 150 , 53 . 2'8 



1900 . 100-0 



Temperature Observations. The following series of temperatures, 

 taken towards the east end of the loch at noon on June 3, 1902, 

 indicates a range of only l-2 Fahr., the greater part of the variation 

 occurring in the upper 10 feet of water: 



Loch Ossiati (see Plate LXXXVL). Loch Ossian (or Ouchan) is 

 a narrow loch in a valley running nearly north-east and south-west to 

 the north of Rannoch moor (see Fig. 55). It lies at a considerable 



