Petroglyphs have seldom been found in the central area of the United States. In the wooded region of the Great lakes characters have been depicted upon birch bark for at least a century, while in the area between the Mississippi river and the Rocky mountains the skins of buffalo and deer have been used. Large rocks and cliffs favorably situated are not common in that country, which to a great extent is prairie. In the general area of these typical groups characters are frequently found which appear intrusive, i. e., they have a strong resemblance not only to those found in other American groups, but are nearly identical with characters in other parts of the world. This fact, clearly established, prevents the adoption of any theory as to the authorship of many of the petroglyphs and thwarts attempts to ascertain their signification. ALASKA. Ensign Albert P. Niblack, U. S. Navy, (_a_) gives a brief account, with sketches, reproduced here as Fig. 4, of petroglyphs in Alaska, which were taken from rocks from the ancient village of Stikine, near Fort Wrangell. Others were found on rocks just above high-water mark around the sites of ruined and abandoned villages. [Illustration: FIG. 4.--Petroglyphs in Alaska.] In the upper character the Alaskan typical style of human faces is noticeable. The lower gives a representation of the orca or whale killer, which the Haida believe to be a demon called Skana, about which there are many mythic tales. Mr. Niblack remarks: In their paintings the favorite colors used are black, light green, and dark red. Whether produced in painting, tattooing, or relief carving, the designs are somewhat conventional. However rude the outline, there are for some animals certain conventional signs that clearly indicate to the initiated what figure is meant. With the brown bear it is the protruding tongue; with the beaver and wolf it is the character of the teeth; with the orca, the fin; with the raven, the sharp beak; with the eagle, the curved beak, etc. ARIZONA. Mr. G. K. Gilbert, of the U. S. Geological Survey, gives the following information concerning petroglyphs observed by him in the vicinity of San Francisco mountain, Arizona: