Kid Flash! said:My guesses.
1.) Because the rocks have eroded and weathered over themselves over time.
2.) Or because the pressure of the rocks from some other force bonded them together.
3.) Or they were freeze-thawed.
Thats my guess, I wouldve been able to answer that last year, because I was in Earth Science and we went over something like that, but I forgot.
I gave my best info.