During this time of initial uplift an amazing process is going on deep underground. A major fault has developed, fracturing the buckled layers of rock. A vast mountain plate begins to slide eastward, over-riding and submerging the rock layers to the east and opening the wide trench that is today the North Fork Valley. Known as the Lewis Overthrust, this gigantic earth-force has created an unusual situation: ancient rock strata lying atop recent rock strata. Now less than 3 minutes of film remain. The arrival of the ice is imminent. We look at the landscape of featureless mountains and wonder at the dramatic difference that this last 3 million years will make. We do not see the familiar forests and lakes, the savage peaks, and the broad, deep valleys of this present land. These mountains are gentle, arid, and shallow-valleyed. The vague outlines are there; we recognize the general alignments of the drainage systems, the bloated domes from which sharp peaks will be cut. The mountains are connected to one another by blunt ridges and smooth saddles, and the shadows they cast are dull, dunelike. Suddenly the ice is there, filling the landscape, with only the mountaintops protruding. Four times in these last 3 minutes of film the ice sheets advance and retreat, each time leaving an altered landscape. Strange lakes and forests fill the gaps between the glacial invasions. Then we see the mountains we now know come into being rapidly, as if the land were being hacked into shape by giant cleavers. After this flicker of Pleistocene time, the film ends, the forests return, and familiar lakes shine beneath the sun again—these lakes and forests we had thought to be timeless. ■ Up springs the morning wind from Hidden Valley, making the nearby alpine fir branches whiz with its passing and shattering the perfect reflection of Bearhat Peak on the pond. From where I sit, it is a short distance to Hidden Pass; so I leave the pond and walk to the overlook to see again the fine basin quarried by an ancient glacier. Hidden Lake, deep, far below, so blue, fits into its cliffed, crooked valley like a polished boomerang. Closely ringed by ridge and peak—distant Sperry Glacier and pointed Gunsight peering up from the southern jumble, and broad Bearhat impossibly close—this lovely lake is almost lost amid such sharp proclamations of rock. Its outlet gorge gives a narrow view across the angled, hidden valleys of Avalanche and McDonald, past the pyramid of Stanton, to the low, faraway undulations of the Whitefish Range. Glaciation is a cruel master of mountains, biting deeply into their bulk and leaving sheer, spectacular contours when the glaciers disappear. The landforms here attest to their power, everywhere exhibiting the effects of glaciation.