Checked my sump pump, what did I see?

For the first time in a year or two, I checked the sump. Lived here 31
years, previous owner, 4 years, never before saw anything in the bottom,
except pebbles. Now I can't see the absolute bottom.


This time a bunch of stuff that looked like dirty ice. Maybe from 1/2 to
1 inch deep, probably obstructing input, because I think it took longer
to drain the sump.

Two 4" corrrugated inputs to sump, one from each direction. One has the
same kind of crud. Looks like an ice chip, about as big as a quarter or
half dollar -- too big to come through the pipe perforations, right? --,
but not translucent or white. Grey maybe. I pick it up and it
crumbles.

What is this stuff?