The filter should say something like D.E, Sand filter or cart on it.

Anyhow, just because it's setting there at the bottom doesn't mean the filter want catch it. The pool just needs a good vacumming. I would keep an eye on the pressure to make sure it's not to high and nor does it get to high while vacuuming that much junk. In some cases, I'll vacuum that stuff to waste, meaning it never goes to the filter but to the drain. Keep in mind this will drain some water from the pool....all of it if you leave if on waste for a while You may want to Back wash the filter if it's a sand before hand or clean it if it's a cart filer after wards. Also they make some Water clearafier thats works pretty good. It attaches to the fine particals in the pool causing them to fall to the bottom and be vacuumed up. .