In the plan of this work a distinction has been made between a petroglyph, as Andree names the class, or rock-writing, as Ewbank called it, and all other descriptions of picture-writing. The criterion for the former is that the picture, whether carved or pecked, or otherwise incised, and whether figured only by coloration or by coloration and incision together, is upon a rock either in situ or sufficiently large for inference that the picture was imposed upon it where it was found. This criterion allows geographic classification. In presenting the geographic distribution, prominence is necessarily (because of the laws authorizing this work) given to the territory occupied by the United States of America, but examples are added from various parts of the globe, not only for comparison of the several designs, but to exhibit the prevalence of the pictographic practice in an ancient form, though probably not the earliest form. The rocks have preserved archaic figures, while designs which probably were made still earlier on less enduring substances are lost. Throughout the world in places where rocks of a suitable character appear, and notably in South America, markings on them have been found similar to those in North America, though until lately they have seldom been reported with distinct description or with illustration. They are not understood by the inhabitants of their vicinity, who generally hold them in superstitious regard, and many of them appear to have been executed from religious motives. They are now most commonly found remaining where the population has continued to be sparse, or where civilization has not been of recent introduction, with exceptions such as appear in high development on the Nile. The superstitions concerning petroglyphs are in accord with all other instances where peoples in all ages and climes, when observing some phenomenon which they did not understand, accounted for it by supernatural action. The following examples are selected as of interest in the present connection. It must be premised with reference to the whole character of the mythology and folk-lore of the Indians that, even when professed converts to Christianity, they seem to have taken little interest in the stories of the Christian church, whether the biblical narratives or the lives and adventures of the saints, which are so constantly dwelt upon throughout the Christian world that they have become folk-lore. The general character of the Christian legends does not seem to have suited the taste of Indians and has not at all impaired their affection for or their belief in the aboriginal traditions.