66 
THE PARALLEL ROADS OF 
in one respect to the same objection as the 
other. What prevented this sheet of water 
from spreading east and west in Glen Spean ? 
If it not only filled Glen Roy, but extended to 
the southern side of Glen Spean immediately 
opposite the opening of Glen Roy, what pre¬ 
vented it from filling the whole of that valley 
also ? In endeavoring to answer this question, 
I found the solution of the mystery. 
The bed of Glen Spean, through its whole 
extent from east to west, is marked, as I have 
said, by glacial action, in rectilinear scratches 
and furrows. This westward track of the 
main glacier is crossed transversely near the 
centre of the valley by two other glacier-tracks 
cutting it at right angles. Upon tracing these 
cross-tracks carefully, I became satisfied that, 
after the surrounding ice had begun to yield, 
after the masses of ice which descended from 
the northern and southern slopes of the moun¬ 
tains into Glen Spean had begun to retreat, 
and to form local limited glaciers, two of those 
lateral glaciers, one coming down from Ben 
Nevis on the southwest, the other from Loch 
Treig on the southeast, extended farther than 
the others and stretched across Glen Spean. 
