THE FRESH- WATER LOCHS OF SCOTLAND. 51 



towards the central portion of the eastern shore. The area of the lake- 

 floor covered by less than 10 feet of water is about 30 acres, and that 

 covered by more than 20 feet of water is about 7 acres, so that about 

 60 per cent, of the bottom is covered by water between 10 and 20 feet 

 in depth. 



Temperature Observations. The following temperatures taken in the 

 position of the deepest sounding show little variation in the temperature 

 of the water : 



Surface 56-l Fahr. 



15 feet 56-0 



30 55-5 



Loch na Ji-OidcJie (see Plate XIX.). Loch na h-Oidche (or na- 

 Houigh) lies about 6 miles to the south-east of Loch Gairloch, and about 

 3 miles from the shores of Loch Maree. The outflowing stream bifurcates 

 about half a mile from the loch one branch flowing into Loch Garbhaig, 

 and thence into Loch Maree, while the other branch flows into Loch Bad 

 an Sgalaig, and thence into Loch Gairloch, so that Loch na h-Oidche 

 may be said to belong both to the Ewe basin and to the Gairloch basin. 

 The district is mountainous, Beinn an Eoin rising from the eastern shore 

 of the loch, and Bus-bheinn from the western shore, to heights exceeding 

 2800 feet, while to the south lie Beinn Dearg (2995 feet) and Beinn 

 Alligin (3232 feet). The loch trends in a north-north-west and south- 

 south-east direction, and is If miles in length, with a maxinmm breadth 

 of nearly half a mile. The superficial area is about 347 acres, or more 

 than half a square mile, while the drainage area is about 3 square miles. 

 The maximum depth of 121 feet was observed approximately near the 

 centre of the loch. The volume of water contained in the loch is estimated 

 at 816 millions of cubic feet, and the mean depth at 54 feet. The loch 

 was surveyed on August 7, 1902, but the elevation above the sea could 

 not be determined; judging from spot-levels on the Ordnance Survey 

 maps the elevation may be about 1250 or 1260 feet above sea-level. 



Loch na h-Oidche forms, on the whole, a simple basin, though with 

 a slight undulation of the lake-floor in the deep water of the northern 

 portion, which isolates a sounding in 100 feet from the main 100-feet 

 basin. The cross-lines of soundings indicate a regularly sloping bottom 

 from the eastern and western shores towards the centre ; but, while the 

 third line of soundings from the northern end attains a maximum depth 

 of 100 feet, the fourth line of soundings farther to the south attains a 

 maximum of only 89 feet. The 100-feet contour- line is thus interrupted 

 by the undulation referred to, but the shallower contours all enclose 

 continuous areas, and coincide approximately with the shore-line, the 

 75-feet basin being over a mile, and the 50-feet basin nearly 1 J miles in 

 length. The flat-bottomed character of the loch is indicated by the figures 

 in the following table, giving the approximate areas between the contour 



