320 SURFACE GEOLOGY. 
an extensive mer de glace with glaciers moving southerly, and, most 
likely, northerly also. McClintock describes boulders at Leopold har- 
bor (North Somerset), and at Graham Moore bay (Bathurst island), 
which have been transported 100 and 190 miles north-east and north- 
west. West of Hudson’s bay, all explorers describe glaciated conditions, 
but give scarcely any data to enable us to learn the direction of the move- 
ment. In Franklin’s first voyage (1819-22), loose stones are described, 
whose “angular forms” militate against their having travelled great dis- 
tances. In his second voyage are quite a number of notices, implying 
transportation in a westerly direction. 
There is a marked difference in the distances to which boulders have 
been transported by the south-west and south-east currents. The latter, 
as indicated heretofore, are not known to have travelled as much as 100 
miles. The average distance may not exceed 12 to 15 miles, and there 
are no boulders in New Hampshire that have come from the north side 
of the St. Lawrence, nor from great distances in Maine on the north- 
east. In Ohio many have come from more than 100 miles. Boulders of 
native copper in Iowa and Wisconsin have travelled from 300 to 465 
miles. The greatest transportation in the north-west region has been 
that of boulders from the Lake of the Woods, 7oo miles towards the 
Rocky Mountains, upon British territory. Transportation upon ice-floes 
or bergs has been greater, as from Canada West to Baton Rouge, La. ; 
but the others were mostly ice-carried. The greater south-west trans- 
portation seems to be connected with topographical features, viz., the 
continuation of this St. Lawrence valley to the south-west and south. 
The distance of observed continuous south-westerly striation from the 
Laurentian highlands to the base of the Rocky Mountains is about 1500 
miles. From central Greenland to the same place it exceeds 2500 miles. 
We have the means for determining approximately the thickness of the 
ice-sheet requisite to cause a flowage. It would require an average 
slope of about one half of a degree to make the ice move reasonably 
fast. This is forty-six feet to the mile, or one foot rise in every 115 
feet of distance, or one mile for every 115. These data would necessi- 
tate an ice-cap 13 miles high if the centre of dispersion were in Labra- 
dor, or 22 miles for the whole distance to central Greenland. Making 
use simply of what would be required to move the ice over New Eng- 
