IlKADQlAliTlJKS jRMY OF TUK POTOMAC, "I .July 14, 1863 . ƒ Leo's army withdrew from its position around Williamsport yesterday and last night, and re-erossed the Potomac by a pontoon bridge at Falling Waters, and flat boats at the Williamsport Ferry. A portion of Gen. Pleasantou's cavalry entered VVilliamsport this morning and captured many prisoners. Lee had previously sent over all his plunder trains, etc., and a general movement was ordercd tliis morning and our columns were in motion at an early hour, but we found the intrenchments vacated. Washington, July 14. The following dispatch has ]ust been received ; HKADQrARTEES ÁKMY OF TíIE POTOMAC, } July 14_3 p. M. J ToH. W. H.%lleck,Gen.-in-Chcf: My cavalry ia now occupying Falling Waters, havin'g overtaken and captured a brigade of iufantry, 1,500 strong, two guns, two caissoub, two battlo flags and a large number of small arms. The enemy is all accross the Potomac. (Signed) G. G. MEADE. HEADQfARTKHS AlitfX OF TUK PeTOMAC, ) Julyl4, 1863. ƒ To II. W. Hallcck, Gon.-in-Chiof : 8:30 P. M. - My cavalry have captured 500 prisoners, additioual to those previously reported. Gen. Pettigrew of the Confedérate army was kil'ed this morning in the attack on the enemy's rear guard. His body is in our hands. (Signed) G. G. MEADE, Maj. Gen. Washington, July 15. Lee effeoted his crossing by means of a boat and tressle bridge at Williams port. A large portion of his force i? undoubtedly well on its way toward Richmond. The roads through Virginia are so heavy as to render pursuit difficult if not impossible.