When, on the evening of the 10th, there comes the startling news that "Jeb" Stuart, with all his daring gray raiders at his back, has leaped the Potomac at Williamsport, and is galloping up the Cumberland Valley around McClellan's right, the provost-marshal is convinced that the bold dash is all due to information picked up under his very nose in the valley of the Monocacy. If he ever had the faintest doubt of the justice of his suspicions as to "Doctor Warren's" complicity, the doubt has been removed. Already, at his instance, a secret-service agent has visited Hastings, and wires back the important news that the doctor left there about the 25th of September, and has not returned. On the 11th he is rejoiced by a telegram from Washington which tells him that, acting on his advices, Doctor Warren had been found, and is now under close surveillance at Willard's. Then it is time for him to look out for his own movements. Having leaped into the Union lines with all his native grace and audacity, the cavalier Stuart reposes a few days at Chambersburg, placidly surveying the neighborhood and inviting attack. Then he rides eastward over the South Mountain, and the next heard of him he is coming down the Monocacy. McClellan's army is encamped about Sharpsburg and Harper's Ferry. He has but few cavalry, and, at this stage of the war, none that can compete successfully with Stuart. Not knowing just what to do against so active and calmly audacious an opponent, the Union general is possibly too glad to get rid of him to attempt any check. To the vast indignation and disappointment of many young and ardent soldiers in our lines, he is apparently riding homeward unmolested, picking up such supplies as he desires, paroling such prisoners as he does not want to burden himself with, and exchanging laughing greetings with old friends he meets everywhere along the Monocacy. At Point of Rocks, whither our provost-marshal and Colonel Putnam are driven for shelter, together with numerous squads of convalescents and some dozen stragglers, there is arming for defence, and every intention of giving Jeb a sharp fight should he attempt to pick up supplies or stragglers from its sturdy garrison. Every hour there is exciting news of his coming, and, with their glasses, the officers can see clouds of dust rising high in air far up the valley. Putnam has urgent reason for wanting to rejoin his regiment at once. What with the information he has received from the two or three officers whom he has questioned, and the papers themselves, he has immediate need of seeing the ex-quartermaster sergeant, Rix. But he cannot go when there is a chance for a fight right here. Stuart may dash in westward, and have just one lively tussle with them to cover the crossing of his valuable plunder and prisoners below. Of course they have not men enough to think of confronting him. Just in the midst of all the excitement there comes an orderly with despatches and letters