330 BATHYMETRICAL SURVEY OF 



visible at certain localities on either side of Loch Creagach, and on the 

 ridges east and west of the lower end of Loch Laoghal, where they pass 

 underneath the sill-like mass of granite and its apophyses. For a 

 distance of upwards of 2 miles from the foot of Loch Laoghal granite 

 occurs on both banks of the lake, but in the southern portion the 

 granite extends continuously along the west side, while the crystalline 

 schists occur at intervals on the east side. 



Though these three lakes are now separated from each other, they 

 may be regarded as one sheet of water, as they are nearly at the same 

 level. The strip between Loch Slaim and Loch Creagach consists partly 

 of moraine matter and partly of the same material arranged in the 

 form of terraces rising to about the 400-feet contour-line. The barrier 

 between Lochs Creagach and Laoghal is composed partly of terraced 

 morainic matter, partly of alluvium brought down by the stream 

 draining the north slope of Beinn's Tomaine, and partly of gravelly 

 material driven along the spit by the prevalent west wind. 



An alluvial terrace, about the 400-feet level, connects the three 

 lakes, thereby indicating that they must have been at one time con- 

 tinuous. This feature does not occur in the upper part of Loch Laoghal, 

 where the unmodified moraines extend downwards to the present shore 

 of the loch. It is not improbable, therefore, that the upper portion may 

 have been occupied by a glacier while the barrier of moraines beyond 

 Loch Slaim was being lowered. 



But though these lakes are ponded back by moraines at the surface, 

 it would appear that the lower portions of Loch Creagach and Loch 

 Laoghal may be rock basins, for at a distance of about 1J miles below 

 Loch Slaim the river Borgie flows over a rocky floor of hornblendic 

 gneiss at a height of 304 feet, while the surface level of the two upper 

 lochs is 369 feet. The difference between these elevations is 65 feet. 

 On referring to the chart of the soundings, it will be seen that the 

 greatest depth of Loch Creagach is 84 feet, of the lower basin of Loch 

 Laoghal 217 feet, and of the upper basin 137 feet. If, then, we assume 

 that the rocky barrier 1J miles below Loch Slaim, near Dailaneas, 

 crosses the valley at the same level (304 feet) underneath the drift, 

 then it follows that the depth of water below the rocky barrier is in 

 the case of Loch Creagach 19 feet, of the lower basin of Loch Laoghal 

 152 feet, and of the upper basin 72 feet. The deepest part of Loch 

 Laoghal occurs where the valley is most constricted, and where the 

 hills on either side are loftiest. 



Although no glacial markings have been found in the immediate 

 neighbourhood of the lochs, the striae in the surrounding district show 

 that the ice-movement during the period of maximum glaciation was 

 slightly west of north. The dispersal of the boulders and the disposition 

 of the moraines indicate that during the later glaciation a confluent 

 glacier moved northwards from the interior, one branch skirting the 



