Besides, why was it not exactly in the middle?
It was much too big and thick-set to be a sleeping vulture.

It was the wrong shape to be any sort of chimney.

It was certainly not a bale of merchandise put up on the roof to dry.

And the longer you looked at it the less it seemed to resemble anything recognizable.

I had about reached the conclusion that it must be a bundle of sheepskins up-ended, ready to be spread out in the morning sun, and was going to cast about for something else to puzzle over, when it moved.