Duh, maybe I should have stated that there seem to be many human remains of comparable age as the depositions. To the best of my knowledge, there has never been a full examination of the cave.
That thin black mat is identical in looks to what I see on the sides of many of the older roads here in Missouri, where they cut into the sides of hills.
I have a feeling that this ‘mat’ is likely predominant across the entire northern continent of America.
Just look at the artificial cliffs where hillsides have been cut along the roads you travel, and I bet you’ll see them as well.