On Thu, 17 Mar 2016 21:36:17 -0500, Jon Elson wrote:

They seem to emerge from under it and spread along the surface, but I
can't confirm that yet as I've resisted disturbing them so far in case
they disintegrate and defy further analysis.
It's a good question, though, and I expect to be able to report back on
this later today. I'll sacrifice one of the patches and find out.