you got a big rock and plopped it in the water , then you got a second and plopped it in the water while you were stepping on the first , then you got a third and plopped it in the water while you were stepping on the second , and so on until you were all the way across the river ( which here , and at this time of year , was less than a foot deep and shaled with tawny sandbars ) with your feet still dry .