That day the work of home-building began. Broken Tooth himself selected a big birch that leaned over the stream, and began the work of cutting through the ten-inch butt with his three long teeth. Though the old patriarch had lost one tooth, the three that remained had not deteriorated with age. The outer edge of them was formed of the hardest enamel; the inner side was of soft ivory. They were like the finest steel chisels, the enamel never wearing away and the softer ivory replacing itself year by year as it was consumed. Sitting on his hindlegs, with his forepaws resting against the tree and with his heavy tail giving him a firm balance, Broken Tooth began gnawing a narrow ring entirely around the tree. He worked tirelessly for several hours, and when at last he stopped to rest another workman took up the task. Meanwhile a dozen beavers were hard at work cutting timber. Long before Broken Tooth’s tree was ready to fall across the stream, a smaller poplar crashed into the water. The cutting on the big birch was in the shape of an hour-glass. In twenty hours it fell straight across the creek. While the beaver prefers to do most of his work at night he is a day-laborer as well, and Broken Tooth gave his tribe but little rest during the days that followed. With almost human intelligence the little engineers kept at their task. Smaller trees were felled, and these were cut into four or five foot lengths. One by one these lengths were rolled to the stream, the beavers pushing them with their heads and forepaws, and by means of brush and small limbs they were fastened securely against the birch. When the framework was completed the wonderful cement construction was begun. In this the beavers were the masters of men. Dynamite was the only force that could hereafter break up what they were building now. Under their cup-like chins the beavers brought from the banks a mixture of mud and fine twigs, carrying from half a pound to a pound at a load and began filling up the framework with it. Their task seemed tremendous, and yet Broken Tooth’s engineers could carry a ton of this mud and twig mixture during a day and night. In three days the water was beginning to back, until it rose about the butts of a dozen or more trees and was flooding a small area of brush. This made work easier. From now on materials could be cut in the water and easily floated. While a part of the beaver colony was taking advantage of the water, others were felling trees end to end with the birch, laying the working frame of a dam a hundred feet in width.