Geopuzzle: What are these things? (UPDATED)
Earlier this year a reader sent me a photograph of some rocks they had come across asking me what I thought they were or might represent. I ended up posting the photograph here as a ‘geopuzzle’ and asked all of you to comment on it with your thoughts (see that post here). It was pretty fun and worked so well that I thought I’d do it again.
A few weeks ago a reader sent me a couple photos of some interesting features in some fine-grained sedimentary rocks near her home in northeastern Oregon Washington. I replied with my own educated guess but would like to see what you all think.
The features of interest in these rocks are the numerous saucer-shaped rocks eroding out of the outcrop.
In the photo above you can see these ‘saucers’ in lower right of photo as float.
Again, look at the lower right of the photo above for another view.
So, add your two cents below and I’ll summarize the consensus on this geopuzzle tonight or tomorrow with an update.
UPDATE (12/8/2009): Well thanks to everybody for ‘playing’. Here is my initial response to the reader regarding these saucer-shaped features:
It’s difficult to tell for sure w/ that photo … but my gut instinct is that the saucer-shaped stones are “concretions”, which are features that form after deposition (sometimes millions yrs after) from differential chemical cementation. The wikipedia page is actually pretty good for this: http://en.wikipedia.org/wiki/ConcretionThat’s just my best guess from that photo and your description … I could be wrong.