Posted: Mar 05, 2010 1:36 pm
To me it looks likes a brittle layer (in the middle), possibly a vein of calcite, has fractured due to compressive forces and a different mineral that is more resistant to erosion or dissolution has been deposited in the fractures. Differential weathering has produced the tooth-like appearance due to the later formed fracture filling material being more resistant.
That sounds like a good explanation. One question I have is, why is there a sharp contrast between the middle layer and the outside? The edges that separate the different types of rock are sharp. They don't appear to have been eroded by water for long.(to me) Could the middle layer with the fractures have formed earlier, and then somehow fused to the sedimentary rocks later?
The second rock, I'm confident that they are fossils. Exactly what kind, I don't know.
They look similar in shape to brachiopods. My current guess now is that they are "reversed image" imprints from the inside of the shell, that got slightly warped.
That might explain why it has bristles.
I'll do my best to have them looked at as soon as possible. I'll also try to get clearer pictures.