During a family trip in the Israeli National Trail in the Pora Stream part (31.496871, 34.770928), I noticed these circular rock marks.

Any idea what are they?

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  • $\begingroup$ Shalom Ahi, looks like fractures, maybe? Not sure if anthropogenic or not. Is this in a wadi? Unlikely to be fossils imo. Ask these guys, they're usually good in Israeli geology. $\endgroup$
    – Gimelist
    Dec 10, 2016 at 22:20
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    $\begingroup$ They look like weak concretions, or maybe rip up clasts. you get weird lump shapes to mudstone as it breaks up becasue variation by chemistry effect strength as strongly as variation by particle size. $\endgroup$
    – John
    Dec 11, 2016 at 20:48
  • $\begingroup$ No scale given... $\endgroup$ Dec 11, 2016 at 21:45
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    $\begingroup$ I agree with the concretion idea. Maybe someone with better understanding than I could post an answer that explains what concretions are and how they form. $\endgroup$
    – haresfur
    Dec 11, 2016 at 22:01
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    $\begingroup$ By the way, the OP didn't mention it, but being familiar with the local geology it is limestone. $\endgroup$
    – Gimelist
    Dec 12, 2016 at 5:56

1 Answer 1


It looks like onion skin weathering. It appears in places with large temperature differences between night and day and associated thermal expansion and contraction of rocks on daily basis. That creates weaker spherical zones, where cracks may form later. I have seen that several times in basalts but not limestones, though.


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