644 D. MILNE HOME ON THE PARALLEL ROADS OF LOCHABER. 
of all the drift beds, there is in our northern latitudes a phenomenon, which, if 
rightly understood, would dispel much of the obscurity that still envelopes the 
history of that period—-I mean that curzous scoring and polishing of the rocky 
bed, on which the drift is found so frequently reposing.” 
On this point, therefore,—viz., the marine origin of the detritus,—there is a 
veneral agreement. But how ahout the smoothing and striation of the rocks 
beneath the detritus ? 
Professor Nicot and Mr JAmiEson ascribe these effects to the action of 
land ice,—not so much to local glaciers, as to glaciation of a more general 
character. 
Professor Nicox thinks that the rocks were smoothed and striated during 
“the general glacial striation of the land.” 
Mr Jamieson thinks that these effects were produced during “ the great land 
glaciation of Scotland.” 
CHAMBERS entertained the same view. 
These authors adopt the idea that, before the submergence of the land, the 
rocks had been ground down, smoothed, polished, and striated, under the 
operation of a great ice sheet which covered the country, as such a sheet now 
covers Greenland. 
According to that view, there could have been no detritus when the rocks were 
thus acted on. Professor Nicou on this point is explicit. He says that the 
“ detrital cover has been formed, s¢nce the general glacial striation of the land.” 
This (he says) “is also proved by the fact that it spreads over the rocks marked 
in this manner.” ‘In Glen Roy, these striated rocks oceur immediately under 
the lines.” “ The old line or parallel road now passes over the rock surface, that 
in a former period was worn and striated by the glacier.” 
This point, that the detrital cover, in which the Parallel Roads are cut, 
lies directly upon the striated rocks, is one of some importance with reference 
to the cause of striation. I therefore add one or two extracts from my own 
notes. “Found a flat on which Roman Catholic Chapel stands, about 100 
feet above Bridge of Roy Inn. At this place, smoothed rocks with scratches 
onthem. Some of the faces of these scratched rocks horizontal, others nearly 
vertical. They rise up abruptly from the flat. They are covered with sand and 
gravel” (Notes, vol. i. p. 8). About 500 yards to the north of the summit 
of Craig Dhu, found smoothed rocks, covered partially by detritus (Notes, vol. 
li. p. 42). 
In farther illustration cf this pot, I give a diagram of a smoothed rock 
(fig. 17.) atthe side of Shelf 4, covered by drift, except where exposed. The 
idea suggested on the spot was that the boulder, as well as the rock, had 
been originally entirely covered by detritus; and that the detritus being removed 
by the water of the lake, the boulder and rock were left exposed. This rock 

