Two more stone industries--the _Levalloisian_ and the “_Mousterian_”--turn up at approximately the same time in the European cave layers. Their tools seem to be mainly in the flake tradition, but according to some of the authorities their preparation also shows some combination with the habits by which the core-biface tools were prepared. Now notice that I don’t tell you the Levalloisian and the “Mousterian” layers are both above the late Acheulean layers. Look at the cave section (p. 57) and you’ll find that some “Mousterian of Acheulean tradition” appears above some “typical Mousterian.” This means that there may be some kinds of Acheulean industries that are later than some kinds of “Mousterian.” The same is true of the Levalloisian. There were now several different kinds of habits that men used in making stone tools. These habits were based on either one or the other of the two traditions--core-biface or flake--or on combinations of the habits used in the preparation techniques of both traditions. All were popular at about the same time. So we find that people who made one kind of stone tool industry lived in a cave for a while. Then they gave up the cave for some reason, and people with another industry moved in. Then the first people came back--or at least somebody with the same tool-making habits as the first people. Or maybe a third group of tool-makers moved in. The people who had these different habits for making their stone tools seem to have moved around a good deal. They no doubt borrowed and exchanged tricks of the trade with each other. There were no patent laws in those days. The extremely complicated interrelationships of the different habits used by the tool-makers of this range of time are at last being systematically studied. M. François Bordes has developed a statistical method of great importance for understanding these tool preparation habits. THE LEVALLOISIAN AND MOUSTERIAN The easiest Levalloisian tool to spot is a big flake tool. The trick in making it was to fashion carefully a big chunk of stone (called the Levalloisian “tortoise core,” because it resembles the shape of a turtle-shell) and then to whack this in such a way that a large flake flew off. This large thin flake, with sharp cutting edges, is the finished Levalloisian tool. There were various other tools in a Levalloisian industry, but this is the characteristic _Levalloisian_ tool.