Looks like yeast to me. I had yeast rafts like that in a batch of Ordinary Bitter that I pulled out the first bottle for tasting yesterday. They collected on the little grooves along the inside of the Grolsch bottles I used. Tilted them slightly each way so it fell to them bottom and then chilled. No problems.
3 Gallon Carboy -
6 Gallon Carboy #1 -
6 Gallon Carboy #2 -
Bottled - Show Mead, Acai Apfelwein, Warm Winds Blond, Vertical Line Pale Ale.
Up next: 2 or 3 different Saisons