i§ 77 -J The Great Ice Age and Origin of the “Till” 235 
their summits, they establish the fa( 5 t that during the 
greatest glaciation of the glacial epoch the ice-streams were 
formed on land and flowed out to sea, just as they now do 
at Greenland, or other parts of the world where the snow- 
line touches or nearly approaches the level of the sea. 
All such streams must have followed the slope of the hill- 
sides upon which they rested and down which they flowed, 
and thus the upper limits of glaciation afford no measure 
whatever of the thickness of the ice upon “ the low grounds 
of Scotland,” or of any other glaciated country. As an ex- 
ample I may refer to Mont Blanc. In climbing this mountain 
the journey from the lower ice-wall of the Glacier de Bos- 
sons up to the bergschrund above the Grand plateau is over 
one continuous ice-field, the level of the upper part of which 
is about 10,000 feet above its terminal ice-wall. Thus, if we 
take the height of the striations or smoothings of the upper 
neve, above the low grounds on which the ice-sheet rests, and 
adopt Mr. Geikie’s reasoning, the lower ice-wall of the Glacier 
de Bossons should be 10,000 feet thick. Its adtual thickness, 
as nearly as I can remember, is about 10 or 12 feet. 
Every other known glacier presents the same testimony. 
The drawing of a Greenland glacier opposite page 47 of 
Mr. Geikie’s book shows the same under ardlic conditions, 
and where the ice-wall terminates in the sea. 
I have not visited the Hebrides, but the curious analogy 
of their position to that of the Lofodens suggests the de- 
sirability of similar observations to those I have made in 
the latter. If the ice between the mainland and the Outer 
Hebrides was, as Mr. Geikie maintains, “ certainly more 
than 2000 feet in thickness,” and this stretched across to 
Ireland, besides uniting with the still thicker ice-sheet of 
Scandinavia, these islands should all be glaciated, especially 
the smaller rocks. If I am right the smaller outlying 
islands, those south of Barra, should, like the corresponding 
rocks of the Lofodens, display no evidence of having been 
overswept by a deep “ mer de glace” 
I admit the probability of an ice-sheet extending as Mr. 
Geikie describes, but maintain that it thinned out rapidly 
seaward, and there became a mere ice-floe, such as now 
impedes the navigation of Smith’s Sound and other portions 
of the Arftic Ocean. The Orkneys and Shetland, with 
which I am also unacquainted, must afford similar crucial 
instances, always taking into account the fadl that the larger 
islands may have been independently glaciated by the accu- 
mulations due to their own glacial resources. It is the 
small rocks standing at considerable distance from the shores 
