Hello guys. I'm very new in fossil collection. Not so long ago I purchased a box with stones, meteorites and fossils at garage sale. Now I'm trying my best to ID what is what. Can you please help me to identify those cross section slabs I posted on photos. Size of bigger slab is 82mm (3.2inch), thickness is 6.6mm (0.26inch). It has distinctive pattern of spiral "oncolite stromatolite dots". All sort of suggestions will be very helpful. Unfortunately no information was left by previous owner of that box. Cheers