Are these fossils or man-made?

The rocks look too old (and natural) for those to be man-made impressions. The only thing left is fossils or mineral inclusions of some type... but they don't look like mineral formations.

Were those rocks transported to your property by construction or mining activity? Or are they native to where you found them? And where were they geologically... do you know anything about the age of the rocks and sub-surface structures in your area?