Wildlife Spotting

http://www.elizawire.com/images/Fossilized%20Coral.jpg I found that link while going through images of fossilized coral, if you look closely the at the picture you can see the bottom piece resembles what you have very closely. Of course you may want to look further into it. I believe that my initial instinct is correct.

I don't think it's a gall. The first one has cavity type areas that are fossilized, which look like coral or even a honey comb. Under the right conditions, a chunk of coral could have been fossilized and, later uncovered and tumbled by the stream over the ages until round and smooth. (this is all speculative) If you found the second rock in the same area and can identify any of those as Salt Water creatures, the theory may be plausible.

Looks much like an oak gall. http://en.wikipedia.org/wiki/Gall_wasp

that's interesting...would be awesome to know what it is