During these operations a wad from Duncan's battery had fired the grass. The wind from the Gulf, nearly parallel to the American front, drove a wall of roaring, crackling flame and a cloud of thick smoke across the plain; and, as the armies could see each other only now and then and in spots, firing had to be suspended for nearly an hour. Meanwhile, believing the Mexican left had given way, Taylor shifted his position behind the screen with a view to advancing. Churchill pushed on by the road nearly to where Torrejón had been; the Fourth Infantry moved up to support him; the Fifth went ahead on the extreme right; the rest of the army made corresponding changes; and as a whole the line diverged now thirty or forty degrees from its original direction, while the wagons came nearly up to it.[8.14] But the Mexican left had not yielded, and so Taylor found when he sent a squadron of dragoons to open the way. To avoid being enfiladed, Arista swung his line forward in excellent order, using the Fourth Infantry as a pivot, and again it stood firm under an artillery fire more destructive than at first. Indeed our Fourth Infantry began to suffer a galling cannonade, and Torrejón again assumed the offensive. Canister from the 18-pounders checked him, however, and after sharp musketry exchanges between the Mexican line and our Artillery Battalion, which had advanced and formed a square, serious infantry operations in this quarter came to an end. As for the artillery, Arista had now used up his 650 cannon balls; but the Americans kept at work until nightfall.[8.14] On our left, however, important events occurred. From the first Captain Duncan's battery, which made two fire-units because handled in sections, played a brilliant and effective rôle, supported by the Eighth Infantry and either Kerr's or May's dragoons, and advancing or retiring as the course of the battle dictated. When Arista's change of front threw his right forward nearly 700 yards and seemed to threaten a flank attack, these pieces became more active and more daring than ever, and under their blasting discharges, aided more or less at this time by the 18-pounders, the Mexicans fell rapidly. Again they grew impatient--not principally because they were suffering so terribly, but because they were inactive, and because hints that Arista had sold them began to arrive from Ampudia's quarter; and finally the extreme right wing broke.[8.14]