44 BATHYMETRICAL SURVEY OF 



is estimated at 374 million cubic feet, and the mean depth at over 42 feet, 

 or nearly one-half of the maximum depth. The Dubh Loch was surveyed 

 at the same time as the Fionn Loch, and the elevation of the lake-surface 

 was, for the same reason, not determined by levelling. 



The conformation of the Dubh Loch is quite a contrast to that of the 

 adjoining Fionn Loch. Except for one or two irregularities of the lake- 

 floor, Dubh Loch forms a simple basin, all the contour-lines, though 

 showing occasional sinuosities, enclosing continuous areas. A bank 

 covered by 2 feet of water occurs in the middle of the loch, about 

 300 yards from the south-east end, surrounded by depths exceeding 

 20 feet ; farther down, a line of soundings running from south to north, 

 towards the entrance of the Allt Bruthach an Easain, showed a rise of the 

 bottom from 43 to 38 and 39 feet, sinking again to 51 feet ; still farther 

 down, another line of soundings running from south to north showed a 

 remarkable rise of the bottom from 65 to 51 and 48 feet, sinking again to 

 the deepest recorded sounding (88 feet), whence the soundings shoaled 

 gradually towards the northern shore. The last-mentioned rise is the 

 more striking, as it was observed in the deepest part of the loch, and in 

 close proximity to the maximum depth. The soundings taken in the wide 

 lower portion of the loch are quite regular, the irregularities above 

 referred to occurring in the upper half of the loch. The areas between 

 the consecutive contour-lines, and the percentages to the total area of the 

 loch, are as follows : 



Feet. Acres. Per cent. 



Oto25 50 ... 24-6 



25 50 78 ... 38-2 



50 75 57 ... 28-2 



Over 75 18 ... 9-0 



203 100-0 



These figures indicate an average slope off-shore much steeper than in 

 the deeper water, and an inspection of the map shows that the 25-feet 

 contour follows aprroximately the shore line, approaching in some places 

 very close to the shore, whereas the 50-feet contour runs, for the greater 

 part of its course, at a considerable distance from shore, while the upper 

 part of the loch is occupied by water less than 50 feet in depth. 



LocJian Eeannach (see Plate XVII.). Lochan Beannach is a small 

 irregular sheet of water lying off the central part of the western shore of 

 the Fionn Loch, into which it flows by a stream less than a quarter of a 

 mile in length. The loch consists of two distinct portions, and, as it was 

 found impossible to get a boat through the passage, the smaller south- 

 eastern portion was not surveyed, the soundings being limited to the larger 

 western portion, which is of very peculiar form, almost encircling a large 

 promontory of land projecting out into the loch from the western shore ; 

 the narrow neck of land connecting the promontory and the shore is less 



