OF THE PARALLEL ROADS OF LOCHABER, 
689 
gravel, forming Unachan Hill, which rises to the height of 613 feet. I traced moraine 
detritus up to the northern base of the hill.* 
While these sub-glacial Till deposits were being formed under the ice at various 
levels, the continued extension of the ice-sheet carried other debris, boulders, and gravel 
on its surface to higher levels. The rolled gravel may have been formed by rivulets 
flowing off the mountain sides and discharging on the ice-sheet, or by streams on the 
ice-sheet itself; or it may have been older gravel from a distance. What, however, 
may be the origin of some of the well-rounded pebbles found on Craig Dhu, and of 
those mentioned by Mi - . Milne Home as occurring on the hills around Glen Gluoy at 
heights of from 1,700 to 1,800 feet, has yet to be determined. 
These questions respecting the conditions of the ice-sheet of Scotland are necessarily 
somewhat speculative, but in our ignorance of the effects produced by the great ice- 
sheet of Greenland, we can only draw our inferences from the residual phenomena in 
districts once similarly covered; and I submit these observations as indicating pro¬ 
bable causes of general application and as indices for further research. 
§ 9. The Level of the Land at the Incoming of the Glacial Period. 
In speaking of the ice-slieet we have considered it only in reference to the levels of 
the country as they at present exist; but when we reflect on the great changes which 
the country has undergone since the early glacial period, we cannot suppose the 
existing levels to be identical with those which obtained at that time. The sub¬ 
mergence of the land to the extent of from 1,300 to 1,500 feet, succeeded by move¬ 
ments of elevation of equal or greater importance, which we know to have taken place 
in the later glacial times, renders it impossible to imagine a return now to the status 
quo ante of the earlier period; and it is almost equally difficult to suppose that the 
relative levels of distant, or even of nearly adjacent, areas can have been maintained. 
The question, therefore, arises whether the land stood lower or higher at the inset¬ 
ting of the glacial period. The observations of Mr. Jamieson show that, immediately 
prior to it, the east coast of Scotland stood at a lower level, for he has found beds, 
which he considers to be of the age of the later Crag deposits, skirting the coast of 
Aberdeenshire at a height of about 200 feet.t These beds, however, extend only a 
few miles inland, and no similar deposits have been met with on the west coast. On 
the contrary, there are grounds for believing, from the occurrence of mammalian 
remains of pre-glacial date, that at about that time part if not the whole of the west 
coast was dry land. Great Britain and Ireland in all probability constituted part of 
the continental area ; and the existence of ice-strise, not only in inland valleys and hills, 
but likewise horizontally along hills and slopes facing the sea, indicating the movement 
* Post, p. 715. 
t Quart. Joum. Geol. Soc., vol. xxi., p. 162, 
4 T 2 
