The president of the united states be, and he hereby is, authorized, whenever in his opinion any reservation or any part thereof of such indians is advantageous for agricultural and grazing purposes, to cause said reservation, or any part thereof, to be surveyed, or resurveyed if necessary, and to allot the lands in said reservation in severalty to any indian explain what congress is trying to do by enacting this law. what does it mean when it says "surveyed or resurveyed? "