It must be admitted that no hermeneutic key has been discovered applicable to American pictographs, whether ancient on stone or modern on bark, skins, linen, or paper. Nor has any such key been found which unlocks the petroglyphs of any other people. Symbolism was of individual origin and was soon variously obscured by conventionalizing; therefore it requires separate study in every region. No interpreting laws of general application to petroglyphs so far appear, although types and tendencies can be classified. It was hoped that in some lands petroglyphs might tell of the characters and histories of extinct or emigrated peoples, but it now seems that knowledge of the people who were the makers of the petroglyphs is necessary to any clear understanding of their work. The fanciful hypotheses which have been formed without corroboration, wholly from such works as remain, are now generally discarded. There is a material reason why the interpretation of petroglyphs is attended with special difficulty. They have often become so blurred by the elements and so much defaced where civilized man has penetrated that they cease to have any distinct or at least incontrovertible features. The remarks relating to Dighton rock, infra, Chap. XXII, are in point. Rock-carving or picture-writing on rocks is so old among the American tribes as to have acquired a nomenclature. The following general remarks of Schoolcraft (_a_) are of some value, though they apply with any accuracy only to the Ojibwa and are tinctured with a fondness for the mysterious: For their pictographic devices the North American Indians have two terms, namely, _Kekeewin_, or such things as are generally understood by the tribe, and _Kekeenowin_, or teachings of the _medas_ or priests and _jossakeeds_ or prophets. The knowledge of the latter is chiefly confined to persons who are versed in their system of magic medicine, or their religion, and may be deemed hieratic. The former consists of the common figurative signs, such as are employed at places of sepulture or by hunting or traveling parties. It is also employed in the _muzzinabiks_, or rock-writings. Many of the figures are common to both and are seen in the drawings generally; but it is to be understood that this results from the figure alphabet being precisely the same in both, while the devices of the nugamoons or medicine, wabino, hunting, and war songs are known solely to the initiates who have learned them, and who always pay high to the native professors for this knowledge.