Some apprehension that the enemy was at least contemplating a speedy retreat was entertained during the night that followed the third bloody day. General Pleasonton, chief of cavalry, urged General Meade to advance in force upon the beaten foe, alleging that they were not only greatly weakened by their losses, but undoubtedly demoralized, in consequence of repulse and probable scarcity of ammunition. To ascertain positively what could be of these probabilities, Pleasonton was directed to make a reconnoissance toward the Rebel rear. Accordingly, several detachments of cavalry were thrust out on different roads, where they rode all night. General Gregg, on our right, went about twenty-two miles on the road to Chambersburg, and returning early on the morning of the fourth, reported that the road was strewn with wounded and stragglers, ambulances and caissons, and general _debris_, which indicated that the enemy was retreating as rapidly as possible, and was passing through a terrible season of demoralization. The testimony of the mute witnesses of disaster was corroborated by that of the many prisoners which easily fell into Gregg's hands. Other expeditions, returning later in the day, had similar reports to render of what they had seen and heard. And now came the time for energetic cavalry movements. While our infantry was resting, or engaged in burying our own and the Rebel dead within our lines, the cavalry was despatched to do all the damage it could upon the retreating Rebel columns. KILPATRICK ON THEIR TRAIL. Kilpatrick, having assembled his immortalized division on the plain at the foot of Round Top, on the morning of the fourth, discoursed to them eloquently for a few moments on the interests of the times. He assured his men that their noble deeds were not passing by unnoticed, nor would be unrequited, and that they were already a part of a grand history. He trusted that their future conduct would be a fair copy of the past. But his pathetic and patriotic accents had scarcely died upon the ear of his brave command, when the shrill bugle-blast brought eager men and grazing horses in line of march. Orders had been received by Kilpatrick to repair as swiftly as possible to the passes in the Catoctin Mountains, to intercept the enemy now known to be flying southward at a rapid rate.