620 D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 
any fruit.” (“Essay on the Physical Features of the Valley of the Minnesota,” 
1874. See also ‘“ American Journal of Science” for 1875, p. 313.) 
2. Another remark to the disadvantage of the detrital theory is, that if there 
was any blockage of that nature, some remains of it should still be extant. 
Dr CHAMBERS says,— 
“Tf the termination of any of the lines were the proper index to the termination of any of 
these alluvially confined lakes, we should expect to see some remnants of the blocking matter 
left at those places, say as hummocks on the sides of the vales with only broken passages 
between. But the lines vanish gradually on the smooth hill-sides, without any particular 
mark to distinguish the spots.” (See “ Margins,” p. 113.) 
This objection, at the best, is one only of probability. The argument is, that 
if there was any detrital blockage, fragments of it, in the forms of hummocks, 
might have been expected to be preserved. But there was little reason 
to expect, looking to the nature of the “ blocking matter,” that any of it would 
be preserved. When this “blocking matter ” was undermined, scooped out, and 
washed away by streams, the probability is that the whole would be removed. 
Rosert CHAMBERS admits that in front of Bohina village (p. 123) “the 
bottom of the valley is filled to a great height with alluvial masses, which 
appear to some as diminishing the difficulty as to barriers.” 
I examined particularly the two places in Glen Roy where the blockages 
are supposed to have existed on the lake theory. _ 
At the part of Glen Roy, where the highest shelf stops, there it is that the 
narrowest part of the valley occurs, and it is therefore a spot favourable for a 
blockage. On Bohuntine hill there is at that spot (I quote from my Notes) “a 
“ cliff of drift which runs down the hill transversally to the valley, and may have 
“been a remnant of the barrier which crossed the valley here.” On the south 
side of the Glen, immediately opposite to the above point, there are “some 
‘detrital mounds on the hill side about 1022 feet above the sea, which may 
“have formed part of the same barrier.” (Notes, vol. i., p. 23.) 
Then at the place further west in Glen Roy “on the north side, where 
“Shelf 3 terminates, there is a large mass of detritus standing out transversely 
“to Glen.” (Notes, vol. ii. p. 34.) 
I give these quotations from my Notes, to show that there is not, as 
CHAMBERS and Darwin state, a total absence of all appearance of detrital 
matter from the hill sides where the shelves stop. When first I saw these long 
mounds of drift I looked upon them as remnants of the blockage. But they 
may be only part of the lake bottom cut up by streams from the hill sides. 
It is proper here to advert to the parts of Glen Roy, probably reached by 
the lakes at its two first subsidences. 
It has been assumed hitherto that the uppermost lake at 1149 feet above the 
sea did not extend further west than Cranachan, because the highest shelf is 

