618 D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 
Mr Jamieson of Ellon (“ Lond. Geo. Soc. Journal,” Vol. xiv. p. 526) has 
described a series of terraces extending on both sides of the Spey, in a lower part 
of its course, viz., at Ballindalloch, Aberlour, Rothes, and Cairnty, over a distance 
of about 25 miles. These terraces slope down with, and therefore have been 
made by, the river. He measured their heights very exactly at Rothes, and 
found them to be there 247 feet above the river. He has described the 
materials composing part of one of these terraces at Rothes in a cliff, thus— 
Loose Sand and Gravel stratified : : . : 30 feet. 
Stratified Sand and Mud . : 4 : : : 7 
Gravel and Sand stratified d : : : , 15%; 
Unstratified Pebbly Clay . : : : Lor 
Stratified Sand and Mud . z : : . ‘ Se 
Base of Bank descending to River . : ; : Ua 
192 feet. 
Mr Jamieson has no hesitation in looking on these beds of detritus as 
having been deposited when the sea prevailed over the country. Since the 
retirement of the sea, they have been cut through by the river, so that the 
height of the cliff, at the foot of which the river runs, shows the enormous 
amount of detritus removed. 
Keeping in view these proofs of the action of rivers in eroding and removing 
detritus, there should be little hesitation in allowing that the blockage of the 
Lochaber lakes may have yielded to the agencies of the streams which 
descended upon them from the high and steep hills surrounding the lakes. 
7. Two objections have been taken to this theory of detrital blockage which 
it is right to notice. 
(1) It is said by Mr Darwin, that if the subsidence of the lake in Glen 
Roy, from the highest level to the next, took place by the wearing down of any 
of the sides of the lake, this wearing down would be at the end of the lake 
where it was discharging its surplus waters, viz., at the head of Glen Roy; 
whereas the wearing down is supposed to have been at the opposite end of 
the lake. If Glen Roy was filled by alake, which when it stood at the highest 
shelf, overflowed at its N.E. end into the valley of the Spey, it is contended 
that the erosion of a deeper channel for the overflow would be at that end where 
there was already a stream fit to effect the work. 
This objection it is not difficult to answer. The erosion and lowering of 
the blockage would occur at that part of the lake banks where the materials 
composing these banks were most susceptible of erosion. 
The col or summit ridge between Glen Roy and the Spey Valley being hard 
Granite rock, it was not so likely to be eroded, as the west end of the lake, if it 
consisted of detritus, which would be easily undermined, cut into, loosened 
and carried off by streams from the hill sides. 

