D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 621 
represented on the maps as stopping there. But on the occasion of my last 
visit to Glen Roy, Mr Jotty and I thought we saw traces of the highest shelf 
on the north-west corner of Craig Dhu, which forms the south side of Glen 
Glaster. 
If this discovery is confirmed, there need have been no blockage at Cran- 
achan. The blockage must have been at two other places,—viz., first across 
Glen Glaster, and secondly across Glen Roy, between Bohuntine and Craig 
Dhu. 
A blockage in Glen Glaster would be very easily accomplished, as the 
width there at the summit level is only one-fourth of the width of Glen Roy 
at Cranachan, and the lake there might not have been deeper than 81 feet. 
A very small barrier would be sufficient at that point. 
A barrier across Glen Roy between Bohuntine and Craig Dhu would 
require no change when the lake subsided from Shelf 2 to Shelf 3, so that in 
that aspect of the case, the blockage is attended with few difficulties. 
The objection to the detrital theory which has been most strongly urged, 
viz., the great height of the required barriers, assumes that Glenroy and all the 
valleys of the district had then the same width and the same depth as now. 
But if the vaileys were still occupied by a large proportion of the detritus 
which originally filled them, that objection is entirely obviated. 
When these Lochaber lakes existed, the sea may still have been from 500 
to 600 feet higher than at present. There are in the district, between Fort 
William and Spean Bridge, a number of remarkable Escars and Flats, at various 
heights up to even 500 feet, which strongly suggest the prevalence of the sea. 
There are in like manner extensive plains to the south of Inverness, at about the 
same level, which have been apparently sea-bottoms. Even in the Great Glen 
itself, there are on its 'sides horizontal water-lines at various heights referable to 
the sea. Now, if when the Glen Roy lakes existed, the sea stood from 500 to 600 
feet higher than at present, all the rivers in the country must have been running 
in channels much higher; and, therefore, at that time the valleys could not have 
been so deep or wide as they now are. 
It is therefore a mistake to assume, that because Shelves 2 and 3 in Glen 
Roy are about 700 or 800 feet above the bottom of the valley, this affords any 
indication of what had been the depth of the valley when the lake existed, or 
of the height of the required barriers. The probability is, that the Glen Roy 
lake was not 100 feet deep. 
Another remark of some weight arises out of this higher level of the sea. If, 
when the Glen Spean lake existed, having a height of 856 feet above the present 
level of the sea, the sea was then 600 or even only 400 feet above its present 
level, the sea must have been close to the detritus which I suppose to have 
formed a blockage of the lake between Teindrish and Aonach. More. This 
