Greetings- I found this rock with kids in Montgomery County, Pa., USA, along creekbed. I believe it's a type of sandstone- the Brunswick and Lockatong formations run through county (apologies-I'm just learning geology, it's red-brown). Curious if this is an animal impression? Footprints are known to be found in the area. Photographed at different angle lights, as it looks so different depending. My son showed at school as a fossil- wanted to give him an informed answer. Thanks so much!