Thought can with difficulty visit the intricate and winding chambers which it inhabits. It is like a river whose rapid and perpetual stream flows outwards—like one in dread who speeds through the recesses of some haunted pile and dares not look behind.
'Speculations on Metaphysics [On the Science of Mind]' (written 1815), in D. L. Clark (ed.) Shelley's Prose (1966)