606 D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 
accumulations. Loch Laggan, Loch Treig,* Loch Lochy, and Loch Arkaig are 
examples. Arkaig is specially interesting, because there is evidence to shew, 
that at some former period it discharged into Loch Lochy by a channel different 
from the present one. The old channel is situated at the N. E. end of the lake, 
and forms a deep dry ravine, called “the Dark Mile.” The present channel of 
discharge is at the S. E. corner. Near the mouth of the lake there is a horizontal 
terrace, about 90 feet above the present surface, formed on detritus, which 
suggests that the lake once stood at a higher level. 
Loch Laggan now discharges its surplus waters by the River Spean, which 
has cut for itself a trench about from 30 to 40 feet below what had been here 
the bottom of the lake. One side of the trench is shown on fig. 4. It 









Wai 
in| 
i 
i 
nen 
WHS 

Fig. 4. 
Loch Laggan (1) now discharging its surplus waters by the River Spean (2). About a quarter 
of a mile below the Loch, the Spean is joined by the River Gulbain (3). Both rivers have 
cut deep trenches through the old bottom of the Lake, viz., the lake which formed Shelf 4. 
forms a cliff running for several hundred yards towards the west, till it joins 
another cliff almost at right angles, which has been formed by the River Gulbain. 
The material cut through by both rivers consists of sand, and fine clay im 
horizontal beds, formerly the bottom of the lake which formed Shelf 4. The 
trench cut by the river would have been deeper, but for rock over which the 
Spean flows where it runs out of the lake. 
In my former paper, I referred to a case somewhat analagous, where a lake 
had subsided from one level to another, and which is kept up at its present: 
level by detritus. This lake is Loch Tulla, about 3 miles long and 1 mile broad, 
situated about 40 miles 8S. W. of Glen Roy. Cuamsers, after I had pointed 
out this lake, as a case supporting my theory, visited it, and in his book on 
Sea Margins admitted the correctness of my statements, as to the horizontality 
* Mr Jaminson (page 250, “London Geo. Soc. Pro.,” 21st January 1863), admits Loch Treig, in its 
outflow, “has not even yet cut its way to the very bottom, for the lake is still partly retained by banks of 
gravel,” 

