Economic article analyzing vertical specialization in the American woolen and worsted industries, using 1904 and 1909 U.S. Census figures on establishments, spindles, looms and combing machines. It describes the carding and combing processes, compares the U.S. industry with England, France and Germany, and discusses the reasons the worsted branch is more specialized than the woolen branch, drawing on Professor Clapham. It ends with the tendency toward separate wool-combing (top-making) mills in the United States.