48 
BATHYMETRICAL SURVEY OF 
Loch Lubnaig originally extended to a point below Coireachrombie, 
about three-quarters of a mile below its present outlet. This point has 
been silted up by the detritus laid down by the Stank and Anie burns. 
The original southern termination of the lake touched the rocky barrier 
formed by the Leny grit. It is worthy of note also, that the level of 
Loch Lubnaig has been lowered about 20 feet by the denuding action of 
the river Leny. 
Loch Katrine . — For a distance of 4 miles, west from Brenachoil Lodge 
to Stronachlachar — about the half of the total length of the loch — this 
lake has a comparatively flat bottom, enclosed by the 400-feet contour- 
line. The deepest sounding in Loch Katrine, 495 feet, is at the eastern 
limit of this basin, nearly due south of Brenachoil. The chart shows 
that the soundings throughout this basin gradually increase in depth 
eastwards to Brenachoil Lodge. The position of the deepest sounding 
is of interest, seeing that the strata which form the floor of the lake at 
this point consist of schistose micaceous grits, to the north-west of the 
epidotic grits Green Beds ”) and the Ben Ledi grits, the two latter 
groups having formed the great rocky barrier at and above the outlet of 
the lake. 
Near the upper end of the loch a rocky barrier crosses the lake from. 
Portnellan by the Black island to Budha Maoil Mhir an-t Salainn. The 
deepest sounding along this barrier is 90 feet, and the shallowest is 48 
feet. On its lower side the 100-feet contour-line well-nigh crosses the 
lake. Above it there is another basin over half a mile in length, the 
greatest depth of which is 128 feet, immediately in front of the rocky 
ridge just referred to. Westwards the lake shallows, and at its head 
it has been silted up for a distance of half a mile by the alluvium laid 
down by the Gyle river. 
Below Brenachoil Lodge the soundings show an uneven floor, due 
probably to ridges of rock rather than to morainic deposits, if we may 
judge from the geological features on both sides of the lake. Ellen’s 
isle is composed of epidotic grits Green Beds ”), and the promon- 
tories of Am Priosan partly of Green Beds ” and partly of Ben Ledi 
grits. The promontory between the pier and the sluice is formed of 
Ben Ledi grits. / 
During the geological survey of that region several small faults were 
found to cross Loch Katrine, but these are of minor importance, and 
have produced locally a slight brecciation of the strata. It is a typical 
example of a rock basin. The deepest sounding occurs in the front of 
the great rocky barrier in the lower part of the lake, in accordance with 
what we might naturally expect on the theory of glacial erosion. 
Though the soundings prove the deepest part of the lake to be 131 feet 
below sea-level, yet this depth is in proportion to the vast thickness of 
the ice during the successive glaciations of the basin. 
Loch Achray . — This lake forms one basin, the deepest part being 
