The Mexican cavalry, about two thousand strong, under command of General Alvarez, was two miles west from Chapultepec on the right of the line.  After a thorough reconnoissance by the American engineer, General Scott on the afternoon of the 7th issued the necessary orders for massing and disposing his army.  The general depot was established at Mexcoac.  One brigade of Twiggs’s division under Colonel Plympton was ordered to move and threaten the city by way of the Nino Perdido road, moving at 6 P.M.  Quitman marched from San Augustin on the 8th to Coyoacan.  Pillow was to advance with one brigade and take command of the advanced position which was held by Twiggs’s division and a part of his own, while Cadwallader was to join Worth.  At Molino del Rey was supposed to be a cannon foundry, and it was thought by General Scott that a large quantity of powder was stored there.  General Worth was ordered to make the attack, carry the enemy’s lines, and destroy the ordnance works and return to his former position.  To carry out this order General Worth directed General John Garland’s brigade to be posted on the right with two pieces of Simon H. Drum’s battery, so as to prevent re-enforcements from Chapultepec, and to be in position to support, if necessary, the assaulting forces; the guns of Captain Benjamin Huger to be placed on the eminence to Garland’s right and rear; a storming party of some five hundred picked men under Brevet Major George Wright, Eighth Infantry, to take post near and to the right of Huger’s battering guns, to attack the battery in the center of the enemy’s lines; Clarke’s brigade under Colonel James S. McIntosh and Captain James Duncan’s battery opposite the enemy’s right to support the assaulting column; Cadwallader to be held in reserve; and Major Edwin V. Sumner with his cavalry to be posted on the extreme left.  Some changes were made in the disposition of the Mexican forces.  Early on the morning of the 8th Huger with two 24-pounders opened fire, and the assaulting column under Major Wright advanced under a heavy fire of grapeshot from the Mexican center and left.  Undismayed, they pushed forward now under fire of musketry, captured a battery, and turned it upon the enemy, who fled in confusion.  They were soon re-enforced, and rallied and reopened fire not only from their lines but from the housetops and walls.  The storming party was driven back, but Duncan’s battery opening fire at this time checked the Mexican advance.  The light battalion of Colonel Charles F. Smith, now under command of Captain Edmund Kirby Smith, Fifth Infantry, moved forward, supported by a part of Cadwallader’s brigade, and this was followed by a forward movement of Garland’s brigade and Drum’s battery.  This movement was irresistible, and the Mexicans fell back, bravely contesting every inch of ground.  Pending the fire of Duncan’s battery, one section of the battery, under Lieutenant Henry J. Hunt, opened fire on the enemy’s lines between the Casta Mata and Molino