Surface Geology of the Yukon Territory. — Norde/iskjold. 295 
4. The Region of Transition. (Lake Lebarge to Fort Sel- 
kirk.) 
The topography of the Yukon territory exerts its chief 
influence upon us through -its relations to the phenomena of 
the glacial period. Nowhere in the world is it possible to study 
to such advantage as here the changes that land ice with its at- 
tendant glaciers brings about. The coast chain was presuma- 
bly at one time completely covered with ice; all even the most 
lofty plateaus are dotted over with erratic blocks and kame-like 
formations are also found. Only the valleys, however, are 
rounded; all the summits rose above the ice for a sufficiently 
long time to assume the characteristic broken and erosive form 
that belongs to all mountain chains that are exposed to the in- 
fluence of great variations of temperature. All round lake 
Marsh, on the other hand, and still more so round lake Le- 
barge all the summits are rounded and polished by the ice. 
which possessed considerable thickness but was, nevertheless, 
in the main body confined to the valleys and which subsequent- 
ly retreated from the district rapidly. The district immediate- 
ly to the north presents features of great interest. The moun- 
tains as elsewhere are bare, while their details are rounded in 
"roches moutonnees" form. Deeply decayed rocks are only to 
be found in well protected narrow valleys. 
North of the Big Salmon river it is only the lower slopes of 
the mountains that preserve this glaciated form, the upper 
slopes being broken and sharply outlined; the boundary be- 
tween these zones that without doubt marks the utmost bight 
the ice attained gets lower and lower. In the neighborhood of 
the Nordcnskjold river it is about 200 feet high; north of the 
F^iv.k rapids no hills rounded by ice are met with. The moun- 
tains are covered with gravel that has arisen from atmospheric 
causes, while where the actual face of the rock projects it is 
often very much broken into pointed pinnacles, probably in 
part attributable to the wind having removed the products of 
atmospheric decay. 
It is evident that a glacier of diminishing thickness towards 
tlie north passed through this valley and came to an end some- 
where north of the Five Mngcr rapids. We have already men- 
tioned the boulder-clay, lying with a covering of sand and 
gravel in the valley-bed in this district. Its appearance is far 
