MACKIE — THE PAEALLEL ROADS OF GLEN EOY. 
125 
between Glen Eoy and Glen Gloy, rising between the two and dis- 
charging its waters on both sides. It is important, Macculloch con- 
tinues, to notice that although the opposite sides of Glen Turit are 
very little dissimilar either in shape or composition, they do not 
equally exhibit equal traces of the roads." 
Glen Eoy itself opens by a wide mouth, varying from five to seven 
miles, into the great valley which stretches from the northern to the 
western sea ; the whole of this space is uneven and hilly. Applying 
the spirit-level to a great many points, Macculloch found them inferior 
to the lowest " road " of Glen Roy, with one or two exceptions. The 
opening of Glen Gloy is narrow. By a comparison of heights, 
Macculloch found that Loch Laggan to the east is depressed 369 feet 
below Loch Spey, and 432 feet below the uppermost "road" of Glen 
Boy. Supposing therefore that the water stood at the highest eleva- 
tion in Glen Roy in the present state of the earth " it would run into 
the Spey not only by the channel of Loch Spey, but by that of Loch 
Laggan also." For these singular roads, Macculloch offered (1817) 
the ingenious solution that they had been formed by the waves, or 
littoral action of standing water. " The absolute water-level," he 
says, " which is found to exist between the corresponding lines both 
in Glen Roy and in those valleys which communicate with it, admits 
of a ready solution on the supposition that a lake once occupied this 
set of valleys ; nor can it be explained on any other. As a free 
communication in one direction at least . still exists among them, it 
would even now be easy to imagine the water replaced in the same 
situation ; the difficulty of confining it will be a subject for future 
consideration. If, however, a lake be considered the cause, it is plain 
that the lines in question were once the shores of the lake ; and it 
equally follows that it had existed at three different elevations, and 
that the relative depths of these three accumulations of water may be 
measured by the relative vertical distances of these three lines from 
the bottom of the valley. Thus the nature of the retaining obstacles 
becomes more complicated, and adds materially to the difficulties." 
Having compared all the appearances of Glen Roy with those 
which are found in existing lakes, and considered the probable changes 
which the drainage of such lakes would effect on these containing- 
valleya, he proceeds to point out the difficulties with which even this 
hypothesis is encumbered. 
" It has been seen," he says, " that considerable deficiencies may be 
observed in the courses of the ' lines,' as well in Glen Roy itself as in 
