BLACKFOOT (Siksika)  , a tribe and confederacy of North American Indians of Algonquian stock . The name is explained as an allusion to their leggings being observed by the whites to have become blackened by marching over the freshly burned prairie . Their range was around the headwaters of the Missouri, from the Yellowstone northward to the North Saskatchewan and westward to the Rockies . The confederacy consisted of three tribes, the Blackfoot or Siksika proper, the Kaina and the Piegan . During the early years of the 19th century the Black-foots were one of the strongest Indian confederacies of the north-west, numbering some 40,000 . At the beginning of the loth century there were about 5000, some in Montana and some in Canada . See Jean L'Heureux, Customs and Religious Ideas of Blackfoot Indians in J . A . I., vol. xv . (1886) ; G . B . Grinnell, Blackfoot Lodge Tales (1892); G .