I recently bought a house with a small mold problem in the attic. I was told it was the result of improper ventilation, and once I fixed that the mold would basically go dormant - or I could choose to have it cleaned. The mold is on the underside of the roof, and is not very severe. However, when I was up there recently, I pulled back the newer insulation that had been laid down, and found what is shown in the picture below. I was told by an insulation guy that it is old cellulose, and some vermiculite, and that I could just cover it all up with new insulation. So my question is, is it OK to just cover this up? Or should it be removed? The old insulation appears to be dark, and I'm concerned it could be mold growth. But the insulation guy said it was just dirt. Regarding the vermiculite, his guess is that they removed most of it but didn't get it all. Regardless, I will be adding proper vents and an attic fan which I believe will help prevent future mold growth.