Inside a parenthesis, Lily thinks of the sea as silk stretched across the bay. She thinks of distance’s power, how it has devoured Mr. Ramsay, Cam, and James so that she feels they have “become part of the nature of things” and are permanently lost. The smoke from an out of view steamship lingers in the air.
Lily’s metaphor turns the sea into a kind of canvas (fabric stretched over a surface). In a perspective similar to Cam’s, Lily feels distance extinguishing the meaning of the Ramsays for her until they are “lost.”