WHat simile does Robert Louis Stevenson use to describe the spyglass?

Here is the only quote with the word "spy glass" in chapter 13:

All were strangely shaped, and the Spy-glass, which was by three or four hundred feet the tallest on the island, was likewise the strangest in configuration, running up sheer from almost every side and then suddenly cut off at the top like a pedestal to put a statue on.