the advanced posts of Las Heras were attacked by the enemy at Pichueta, on the eastern slope of the Cordillera. A reinforcement under Major Martinez drove the Royalists, after two hours' fighting, across the summit. San Martin, on hearing of this, at once despatched Major Arcos with 200 men to seize the pass of Achupallas. On the 4th February Arcos found the guard there strongly reinforced; he attacked at once, and the day was decided by Lieutenant Juan Lavalle, of the mounted grenadiers, who here led the first of those desperate charges of cavalry for which he was afterwards so renowned.
At three in the morning of the 2nd February Las Heras crossed the summit of the Cordillera, and on the 4th, at sundown, an advanced post of the Royalists at Guardia Vieja was attacked by Major Martinez, and carried at the point of the bayonet; after which Las Heras, in obedience to express orders from San Martin, retired upon his reserve. On the 5th the alarm was given in the valleys of Putaendo and Aconcagua by the fugitives from Guardia Vieja and Achupallas, but Atero, deceived by the countermarch of Las Heras into the idea that he was in full retreat, left the pass of Uspallata open, and marched with 700 men to meet the invaders at Achupallas. Thus, without further trouble, Las Heras debouched on the 8th on to the plain and occupied Santa Rosa.
Soler, with the escort and two squadrons of grenadiers, had hurried on to the assistance of the small force at Achupallas, and thence on the 6th descended into the valley of Putaendo with all his cavalry. Necochea was then detached with 100 men of the escort against the town of San Felipe. On the morning of the 7th he was met by Atero, and, by feigning to retreat in the face of such superior numbers, induced the Royalist leader to follow him up the valley with 300 horsemen, leaving his guns and infantry in a strong position on high ground behind him. When he had drawn him well away from his reserve, Necochea suddenly wheeled his men into line and
