Mark's photo dated 9-25
I'll take a stab at this and hopefully others will chime in as well. This makes me think of hydraulics. A friend of mine is an avid whitewater kayaker and in his training and experiences the term hydraulics comes into play. This is what one can encounter while kayaking the whitewaters. It comes into play near waterfalls and large boulder areas. If not trained properly it can end your life. The hydraulic can keep you pinned under water and eventually end your kayaking days. To avoid such a situation the kayaker will roll up into a ball and will be spit out of the hydraulic most of the time. So seeing your round rock made me think of the hydraulic effect. It could be possible that your rock may have had such an experience over a long period of time. Eventually rounding out to the point of being spit out of such a situation. Or the source of this action just dried up. I cannot say with certainty that this is just what happened but it is a possibility. Just a thought, Ward.
From Ward - September 27, 2012 at 23:38:05