One of the most compositionally daring works in the collection — a vast white field occupying roughly the upper three-quarters of the picture, above a thin strip of earth and a narrow zone of dense abstract marks at the very bottom. The composition is structured in three horizontal registers: sky (nearly white, with barely-suggested pale blue cloud forms), earth (a thin yellow-ochre and blue band), and underworld (a narrow zone of dense dark marks at the base).
That bottom zone is the most extraordinary element. Dense, convoluted line-work in dark purple-brown fills the lowest portion of the composition — interlocking curved lines, spiral forms, small face-like and creature-like elements packed tightly together. This is Sidney's most complex linear passage, rendered at a scale that makes it nearly illegible as individual forms. It reads as the substrate of the world — what lies beneath the surface, visible only from this edge-on perspective.
The contrast between the vast pale sky above and the dense dark complexity below is the work's visual argument: the visible world is mostly emptiness and light, but beneath the surface lies this — dense, intricate, teeming. The thin strip of earth between them is the membrane.
The title names what the composition depicts: the edge of the world, seen in cross-section, the sky above and the underworld below with only a thin line of reality separating them.