In "The Song of Flying Fish" by G. K. Chesterton, the author was describind the dreams of someone, saying:
Boyle, being young, was naturally both the healthier and the heavier sleeper of the two. Though active enough when he was once awake, he always had a load to lift in waking. Moreover, he had dreams of the sort that cling to the emerging minds like the dim tentacles of an octopus. They were a medley of many things, including his last look from the balcony across the four grey roads and the green square. But the pattern of them changed and shifted and turned dizzily, to the accompaniment of a low grinding noise, which sounded somehow like a subterranean river, and may have been no more than old Mr. Jameson snoring in the dressing-room.
What's meant here by "pattern", I mean how "pattern" can turn to "noise"?