The Indians of the Great Plains lived a very different life from that of the natives of either the mountains or the Pacific coast. In the far north, to be sure, the rigorous climate caused all the Indians to live practically alike, whether in the Rockies, the plains, or the Laurentian highland. South of them, in that great central expanse stretching from the latitude of Lake Winnipeg to the Rio Grande River, the Indians of the plains possessed a relatively uniform type of life peculiar to themselves. This individuality was due partly to the luxuriant carpet of grass which covered the plains and partly to the supply of animal food afforded by the vast herds of buffaloes which roamed in tens of thousands throughout the whole territory. The grass was important chiefly because it prevented the Indians from engaging in agriculture, for it must never be forgotten that the Indians had neither iron tools nor beasts of burden to aid them in overcoming the natural difficulties in the way of agriculture. To be sure, they did occasionally pound meteoric iron into useful implements, but this substance was so rare that probably not one Indian in a hundred had ever seen a piece. The Indians were quite familiar with copper, but there is not the slightest evidence that they had discovered any means of hardening it. Metals played no real part in the life of any of the Indians of America, and without such tools as iron spades and hoes it was impossible for them to cultivate grassland. If they burned the prairie and dropped seeds into holes, the corn or beans which they thus planted were sure to be choked by the quickly springing grass. To dig away the tough sod around the hole for each seed would require an almost incredible amount of work even with iron tools. To accomplish this with wooden spades, rude hoes made of large flakes of flint, or the shoulder blades of the buffalo, was impossible on any large scale. Now and then in some river bottom where the grass grew in clumps and could be easily pulled up, a little agriculture was possible. That is all that seems to have been attempted on the great grassy plains.