Judge Richard Posner has suggested that the legal system in the United States has developed along the lines of a cartel. That cartel formed, in large part, first because of changes in the training of lawyers and then because of resulting changes in the licensing of lawyers. Throughout the 19th century, educational standards rose and a movement to make the practice of law a restricted occupation started to develop. Posner and others date the beginnings of this movement to 1870, when Christopher Columbus Langdell—the then-dean of Harvard Law School—revolutionized legal education. Langdell believed that law was a science and that opinions written by appellate judges were the raw materials of this branch of science. So, in Langdell's view, just as geologists study rocks and zoologists study animals, lawyers should study published case opinions through a lengthy curriculum. And for the new system to jell completely, it required the abolition of the centuries-old practice of prospective lawyers entering the profession through a process of apprenticeship combined with self-study ("reading law").