I reported the cause of the delay to General Smith and requested instructions to rejoin my company; but he said he desired that I should remain with him for a while. By his order, the three brigades were soon put in motion. I again asked him to permit me to rejoin my proper command. He replied "Not yet" and added: "I will soon give you instructions". Because of a dense fog the delay in reaching the position in rear of the Mexican works was no material disadvantage. The fog began to disappear about the time I reported to General Smith. He was then on a ridge at a point, about 600 yards in rear of the Mexican works. The three brigades were passing around the extremity of that ridge, several hundred yards in rear of the General. All was quiet in the lines of the enemy. There was another ridge south of the one on which General Smith was standing, and separated from it by a deep and very narrow valley. The sides of both ridges were precipitous; their tops sloped gently to the enemy's line. General Smith informed me that Riley's brigade would pass partly beyond the extremity of the second ridge; then face to the left, and attack a strong Mexican detachment which was in position on that ridge, several hundred yards in rear of their works. Riley was ordered to drive that detachment and pursue it closely into the Mexican main lines. Cadwallader's brigade would go on when Riley faced to the left; and, as soon as he passed Riley, Cadwallader would also face to the left and come into action on Riley's right. Smith's own brigade would turn to the left before reaching the extremity of the second ridge. The Third Infantry and First Artillery would advance in the deep valley between the two ridges; whilst the Rifle Regiment, with the engineer company leading, would ascend the steep slope of the second ridge, and get into position on the flank, or rear, of the Mexican detachment which Riley was to attack in front. In the meantime the head of Smith's brigade had come within view, near the foot of the steep slope of the second ridge, and was moving towards the Mexican main line. General Smith pointed out to me the route to be taken to reach the top of the second ridge; and ordered that the engineer company and rifles should bear to the right, and on getting near the Mexican detachment, remain concealed, and quiet, until Riley's brigade became well engaged; then join in the attack and pursuit of that detachment. With these specific instructions, I was ordered to rejoin my company; and Lieutenant Beauregard was directed to take general charge of the movements of Smith's brigade. When Beauregard and I reached the top of the second ridge we found we were 50 yards, or less, in rear of the Mexican detachment, which was facing Riley. All was quiet. In a very few moments Riley's fire commenced.