It is not probable that much valuable information will ever be obtained from ancient rock carvings or paintings, but they are important as indications of the grades of culture reached by their authors, and of the subjects which interested those authors, as is shown in the appropriate chapters following. Some portions of these pictures can be interpreted. With regard to others, which are not yet interpreted and perhaps never can be, it is nevertheless useful to gather together for synoptic study and comparison a large number of their forms from many parts of the world. The present collection shows the interesting psychologic fact that primitive or at least very ancient man made the same figures in widely separated regions, though it is not established that the same figures had a common significance. Indications of priscan habitat and migrations may sometimes be gained from the general style or type of the drawings and sculptures, which may be divided into groups, although the influence of the environing materials must always be considered. The more modern specimens of picture-writing displayed on skins, bark, and pottery are far more readily interpreted than those on rocks, and have already afforded information and verification as to points of tribal history, religion, customs, and other ethnologic details. A criticism has been made on the whole subject of picture-writing by the eminent anthropologist, Dr. Andree, who, in Ethnographische Parallelen und Vergleiche (_a_), has described and figured a large number of examples of petroglyphs, a name given by him to rock-drawings and now generally adopted. His views are translated as follows: But if we take a connected view of the petroglyphs to which the rock pictures, generally made with red paint, are equivalent, and make a comparison of both, it becomes evident that they are usually made for mere pastime and are the first artistic efforts of rude nations. Nevertheless, we find in them the beginnings of writing, and in some instances their transition to pictography as developed among North American Indians becomes evident.