50 
BATHYMETRICAL SURVEY OF 
far from the outlet. On this flat there are moraines rising up in the 
midst of the alluvium. The greatest depth of the loch is 67 feet. At 
the upper or east end, where the loch is shallow, two islets appear, one 
formed of solid rock and the other of moraine matter. 
The soundings of the various lakes in the basin of the Teith above 
Callander, when viewed in connection with the geological structure 
and glacial phenomena of that area, furnish strong evidence in support 
of the theory of their excavation by ice-action. It is probable that, 
though the lakes lie, as a rule, across the path of the great mer de glace, 
they may have been partially eroded by that ice-sheet; at the same 
time there can be little doubt that their final modification must have 
been produced by the large valley-glaciers. 
The other lochs surveyed may be briefly characterised as follows : — 
Loch Chon . — Loch Chon is a striking example of a rock basin. The 
upper portion of the lake is floored by mica-schists, and the lower 
portion by the Ben Ledi grits and schistose epidotic grits Green 
Beds ”), the members of the two latter groups being repeated by sharp 
folds. The trend of the loch — N.N.W. and S.S.E. — is oblique to the 
strike of the strata. At the head of the lake there is a broad alluvial 
flat, where it has been silted up for a distance of one-third of a mile by 
the detritus laid down by the adjacent streams. In the northern part 
of the basin the deepest soundings vary from 33 to 37 feet; but at a 
point about half a mile below the present head of the lake the depth 
increases from 40 to upwards of 60 feet. This feature coincides with a 
line of fault that crosses the loch in a north-east and south-west 
direction, its downthrow being to the south-east. From this point 
southwards for half a mile there is a narrow basin enclosed within 
the 50-feet contour-line, and within this basin there is a narrow trough, 
about 100 yards long and upwards of 75 feet deep, near the west 
margin of the lake. There is ground for the belief that nearly the whole 
of the basin bounded by the 50-feet contour-line is floored by mica- 
schist. 
About a mile below the head of the lake the soundings prove a 
remarkable decrease in the depth, the 25-feet contour-line near the 
Heron islands being deflected towards the centre of the loch. The 
shallowing of^the basin here takes place along the outcrop of very 
massive epidotic grits Green Beds several glaciated rocky islands 
appearing along this line. Southwards to the mouth of the lake there 
are alternations of Ben Ledi grits and schistose epidotic grits, the 
narrowest parts of the lake coinciding with the exposures of the latter 
group. 
About 100 yards below the outlet of the lake a prominent band of 
schistose epidotic grits occurs, which evidently formed a rocky barrier 
during the glaciation of that region. Beyond this outcrop there is a 
