On September 7 both the Fifth and Sixth French Armies were heavily engaged on our flank. The Second and Fourth Reserve German Corps on the Ourcq vigorously opposed the advance of the French toward that river, but did not prevent the Sixth Army from gaining some headway, the Germans themselves suffering serious losses. The French Fifth Army threw the enemy back to the line of the Petit Morin River after inflicting severe losses upon them, especially about Montceaux, which was carried at the point of the bayonet. The enemy retreated before our advance, covered by his Second and Ninth and Guard Cavalry Divisions, which suffered severely. Our cavalry acted with great vigor, especially General De Lisle's brigade, with the Ninth Lancers and Eighteenth Hussars. [Sidenote: Germans retreat September 8.] On September 8 the enemy continued his retreat northward, and our army was successfully engaged during the day with strong rearguards of all arms on the Petit Morin River, thereby materially assisting the progress of the French armies on our right and left, against whom the enemy was making his greatest efforts. On both sides the enemy was thrown back with very heavy loss. The First Army Corps encountered stubborn resistance at La Tretoire, (north of Rebais.) The enemy occupied a strong position with infantry and guns on the northern bank of the Petit Morin River; they were dislodged with considerable loss. Several machine guns and many prisoners were captured, and upward of 200 German dead were left on the ground. [Sidenote: Forcing of Petit Morin September 9.] The forcing of the Petit Morin at this point was much assisted by the cavalry and the First Division, which crossed higher up the stream. Later in the day a counter-attack by the enemy was well repulsed by the First Army Corps, a great many prisoners and some guns again falling into our hands. On this day (September 8) the Second Army Corps encountered considerable opposition, but drove back the enemy at all points with great loss, making considerable captures. The Third Army Corps also drove back considerable bodies of the enemy's infantry and made some captures. [Sidenote: British First and Second Army Corps forced passage of Marne.] On September 9 the First and Second Army Corps forced the passage of the Marne and advanced some miles to the north of it. The Third Corps encountered considerable opposition, as the bridge at La Ferte was destroyed and the enemy held the town on the opposite bank in some strength, and thence persistently obstructed the construction of a bridge; so the passage was not effected until after nightfall. During the day's pursuit the enemy suffered heavy loss in killed and wounded, some hundreds of prisoners fell into our hands and a battery of eight machine guns was captured by the Second Division. [Sidenote: Sixth French Army heavily engaged west of River Ourcq.]