GEOGRAPHY: W. M. DAVIS 
701 
Oreille glacier, and as the lake must have been at its highest level when 
the branch glacier had its greatest length, it follows that the erosive work 
of the glacier in truncating the lower ends of the valley-side spurs must 
have been done under water. The glacier seems to have remained im- 
mersed in the lake that it barred because the ice pressed so heavily against 
the bottom and sides of the valley that no water could enter there to 
buoy it up. The lake waters at the end of the branch glacier must have 
been about 1500 feet deep. The same appears to be true of the much 
broader Canadian glacier in Flathead basin, while it was scouring off 
the spur-ends on the western slope of the Mission range.^ The alterna- 
tive supposition that the glaciers were ordinarily floated up from their 
valley floors when the lake waters rose, and that they rested on the 
FIG. 4. A SIDE VALLEY BARRED BY A MORAINE, AT PARADISE, MONTANA, LOOKING NORTH. 
floors and did their erosive work only while the lake was temporarily 
discharged by leaking through the ice barrier, is, apart from its inherent 
improbability, not acceptable because the great terminal moraine 
deposited by the Flathead glacier is of too regular a pattern to have 
been formed by an agency acting so irregularly. 
But the first supposition, on which we are thus thrown back, must 
also seem inherently improbable; and all the more so when the un- 
favorable conditions that it imposes on the Clark-fork branch glacier 
are clearly conceived. This long glacier not only had to creep up a 
relatively narrow valley that sloped against the direction of glacial 
advance; it had to creep up the valley against the weight of the lake 
water in which it was immersed. It is difficult to imagine how the push 
