As soon as the French had assembled in sufficient force at Charleroi, NAPOLEON ordered Count PAJOL to detach General CLARY's Brigade towards Gosselies, and to advance with the remainder of the First Corps of Reserve Cavalry towards Gilly. General CLARY, with the 1st French Hussars, reached Jumet, on the left of the Brussels road, and only but little more than a mile from Gosselies, before the First Prussian Brigade had crossed the Piéton. He now advanced to attack Gosselies, but was met by Lieutenant Colonel LÜTZOW and his Dragoons, who defeated and repulsed him, and thus secured for General STEINMETZ time to pass the Piéton; and as soon as the latter had turned the Defile of Gosselies, Colonel RÜCHEL with the 29th Regiment moved off to rejoin the Third Brigade. The check thus experienced by General CLARY led to his being supported by Lieutenant General LEFÈBVRE-DESNOUETTES, with the Light Cavalry of the Guard and the two Batteries attached to this force; and a Regiment from Lieutenant General DUHESME's Division of the Young Guard was advanced midway between Charleroi and Gosselies as a Reserve to LEFÈBVRE-DESNOUETTES. The Advanced Guard of REILLE's Corps, which had crossed the Sambre at Marchienne au Pont, was also moving directly upon Gosselies, with the design both of cutting off the retreat of ZIETEN's troops along the Brussels road, and of separating the Prussians from the Anglo-Allied Army. D'ERLON's Corps, which was considerably in the rear, received orders to follow and support REILLE. General STEINMETZ, upon approaching Gosselies, and perceiving the strength of the Enemy and the consequent danger of being completely cut off, with the utmost promptitude and decision directed the 2nd Battalion of the 1st Westphalian Landwehr to march against the Enemy's Left Flank, with a view to divert his attention and to check his advance, while, protected by the 6th Lancers and the 1st Silesian Hussars, he continued his retreat towards Heppignies. This plan was attended with complete success; and STEINMETZ reached Heppignies with scarcely any loss, followed by General GIRARD at the head of the Seventh Division of the Second French _Corps d'Armée_, with the remainder of which REILLE continued his advance along the Brussels road. Heppignies was already occupied by the 2nd and 3rd Battalions of the 12th Prussian Regiment, and with this increase of strength STEINMETZ drew up in order of battle, and upon GIRARD's attempting to force the place, after having previously occupied Ransart, he advanced against him, and drove him back in the direction of Gosselies. A brisk cannonade ensued, which was maintained on the part of the Prussians, only so long as it was deemed necessary for covering their retreat upon Fleurus. * * * * *