... on expeditions before the enemy's advance was known, not to rejoin us until the 7th. I had somewhat over one hundred men under me, and was to have formed the rear-guard of cavalry for Sigel's and Asboth 's divisions, but, owing to delay on the part of other cavalry, ordered for advance-guard, the arrangement was suddenly changed at three A. M., we having been ordered to be ready to march at two A. M....