Thanks, Ken. Here’s what I have from a friend who is a retired geology professor: “I presume the patterns are due to shrinkage, but why sometimes straight and sometimes curved, I can’t say! Quite beautiful!” So, shrinkage; I’d never considered that. (Rocks shrink?)
And all the curves inside the big one – I think water or moisture is factor here maybe. Such beautiful colors, too – I love finding these overlooked details so close at hand – thank you!
You’re welcome, Lynn. A retired-geology-professor friend of mine says the cracks indeed have to do with losing moisture. Shale starts out as mud, so that makes sense to me. I’d like to know the time scale on this, though: at what point in the “life” of this shale did it develop cracks?
UPDATE OF SEPTEMBER 20: My friend has spoken with another geology professor, who thinks that the cracks are a recent feature, produced when rushing water erodes covering layers of shale and earth. The cracks, he says, are an adjustment to the new, lowered compression rather than being due to dewatering in the early stages of compaction.
Romancing Reality 
I can’t explain it either, Linda, but it makes a wonderful photo.
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September 10, 2014 at 3:43 PM
Thanks, Ken. Here’s what I have from a friend who is a retired geology professor: “I presume the patterns are due to shrinkage, but why sometimes straight and sometimes curved, I can’t say! Quite beautiful!” So, shrinkage; I’d never considered that. (Rocks shrink?)
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September 11, 2014 at 9:50 AM
And all the curves inside the big one – I think water or moisture is factor here maybe. Such beautiful colors, too – I love finding these overlooked details so close at hand – thank you!
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September 13, 2014 at 6:19 PM
You’re welcome, Lynn. A retired-geology-professor friend of mine says the cracks indeed have to do with losing moisture. Shale starts out as mud, so that makes sense to me. I’d like to know the time scale on this, though: at what point in the “life” of this shale did it develop cracks?
UPDATE OF SEPTEMBER 20: My friend has spoken with another geology professor, who thinks that the cracks are a recent feature, produced when rushing water erodes covering layers of shale and earth. The cracks, he says, are an adjustment to the new, lowered compression rather than being due to dewatering in the early stages of compaction.
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September 13, 2014 at 9:05 PM
That’s such a precise curve too.
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September 15, 2014 at 11:56 AM
Isn’t it? Amazing.
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September 15, 2014 at 12:34 PM