Beneath is a wide plain of billowy mist,
As a lake, paving in the morning sky,
With azure waves which burst in silver light,
Some Indian vale. Behold it, rolling on
Under the curdling winds, and islanding
The peak whereon we stand, midway, around,
Encinctured by the dark and blooming forests,
Dim twilight-lawns, and stream-illumined caves,
And wind-enchanted shapes of wandering mist;
And far on high the keen sky-cleaving mountains
From icy spires of sun-like radiance fling
The dawn, as lifted Ocean's dazzling spray,
From some Atlantic islet scattered up,
Spangles the wind with lamp-like water-drops.
The vale is girdled with their walls, a howl
Of cataracts from their thaw-cloven ravines,
Satiates the listening wind, continuous, vast,
Awful as silence. Hark! the rushing snow!
The sun-awakened avalanche! whose mass,
Thrice sifted by the storm, had gathered there
Flake after flake, in heaven-defying minds
As thought by thought is piled, till some great truth
Is loosened, and the nations echo round,
Shaken to their roots, as do the mountains now.
Shelley, Prometheus Unbound, Act 2, Scene 2.3, lines 19-42. The lines starting "Hark! the rushing snow!" are fairly famous as a description of enlightenment and revolution. Thought can thunder through the nations, shaking them to their roots. But, as good poetic images often do, I think the image goes beyond Shelley's intent; the avalanche is awakened by the Sun.
