Please help, does anyone know what this Fossil may be?

[Important.email.mja]

I found this in Casselman River in Rockwood Pennsylvania a few years back just laying in the middle of the river as I was walking through it trying not to slip on the rocks haha! Always thought it was an intriguing & unique find but still to this day I have no idea what it is. No one whom I've showed it to over the years could identify it either.  Needless to say, we're not expirenced in fossils none the less! I just stumbled upon this site and thought to myself how great it would be to have it finally identified after all these years (found it in 2014)  so I figured I'd post some photos and anticipate receiving some exciting feedback! Any insight at all would be so very much appreciated, and I thank you for taking the time to give it a look & read my post! Thank you so much and take care!! 

[Rockwood]

Given my handle I have to take a shot.   Chert would be my thought.