For reply Red spurred forward and they rode down the steep hill at a canter, which soon changed to a gallop, then to a dead run. Suddenly there came a roar that shook them and the storm broke in earnest, the rain pouring down in slanting sheets, drenching them to the skin in a minute, for their slickers were no protection against that deluge. Hopalong stripped his off, to see it torn from his grasp and disappear in the darkness like a frightened thing. "Go, then!" he snapped. "I was roasting in you, anyhow! I won't have no clothes left by th' time I hits th' Bend--which is all th' better for swimming." Red slackened pace, rode at his friend's side, their stirrups almost touching, for it was safer to canter than to gallop when they could not see ahead of them. The darkness gradually lessened and when they got close to the dam they could see as well as they could on any dull day, except for a distance--the sheets of water forbade that. "What's that?" Hopalong suddenly demanded, drawing rein and listening. A dull roar came from the dam and he instinctively felt that something was radically wrong. "Water, of course," Red replied, impatiently. "This is a _storm_," he explained. Hopalong rode out along the dam, followed by Red, peering ahead. Suddenly he stopped and swore. "She's _busted_! Look there!" A turbulent flood poured through a cut ten feet wide and roared down the other side of the embankment, roiled and yellow. "Good G-d! She's a goner shore!" cried Red excitedly. "It shore is--_No_, Red! It's over th' stone work--see where that ripple runs? We can save it if we hustle," Hopalong replied, wheeling. "Come on! Dead cows'll choke it--get a move on!" When Buck had decided to build the dam he had sent for an engineer to come out and look the valley over and to lay out the lines to be followed. The west end, which would be built against the bluff, would be strong; but Buck was advised to build a core of rubble masonry for a hundred feet east of the centre, where the embankment must run almost straight to avoid a quicksand bottom. This had been done at a great increase over the original estimate of the cost of the dam, but now it more than paid for itself, for Antonio had dug his trench over the rubble core--had he gone down a foot deeper he would have struck it and discovered his mistake.