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 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 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 
