Further research has shown me that green and blue and black are related and that to a degree green and blue are interchangeable. Blue is regarded as a darkened green; that is, green removed from the light, not deepened in hue. Blue, therefore, stands intermediate between green which has the light on it; and blue shaded into black, which has no light on it. In some ceremonies green typifies the earth; in others blue is the symbol. The sky is sometimes represented by green, and again blue is used, while blue darkened to black stands for the destructive elements of the air. I have found a subtle connection between the elements of earth and air that answers somewhat to the blending of the symbolic colors just spoken of. This connection is revealed in the reciprocal or complementary functions of gentes belonging to these two great divisions represented in the tribal structure, as well as in the reactionary character of the elements themselves as portrayed in the myths and typified in some ceremonies. For instance, the eagle mythically belongs to the air, and is allied to the destructive powers of the element and to wars upon the earth, yet the Eagle gens, although connected with the air division of the gentes, is in some tribes a peace gens. An enemy escaping to the tent of an Eagle man is safe and cannot be molested. In symbols eagle feathers are not only the pride and emblem of the warrior but they are essential in certain ceremonies of amity and peace-making. A study of the position of gentes belonging to the divisions of earth and air, their tribal and ceremonial duties, together with their mythological significance, shows lines connecting the gentes of the earth with the gentes of the air which are vertical, so to speak, and might be represented as running north and south on the tribal circle, and indicating mediating offices as between contending or opposite forces. It would occupy too much space to fully set forth my reasons for thinking blue-black to be the symbol of the thunder rather than red and yellow. Although thunder is allied to the four quarters, to the four elemental divisions and partakes of their symbolism, still a study of thunder myths, thunder-names, and the tribal offices of thunder gentes seems to me, at my present understanding of them, to indicate the blue-black as the persistent symbol. I would not at this date make any unqualified statement giving green, blue, or black as the symbol of the west, the water, or the moon; and although in some instances these colors occur in connection with these objects of reverence, I am now inclined to class these as incidental rather than as representative of the color symbols.