In a few years the carriers on the Columbia enjoyed an immense and profitable traffic in the transportation of miners and their supplies. Professor Trimble's description of steamboating on the rivers of the Inland Empire is intensely vivid and interesting. In 1861 came the great movement of miners into these new fields. Among the most important of the localities they entered were the Nez-Perce and Salmon-River districts in northern Idaho. A swiftly accelerating stream of travel started in 1861 for the new mines. A new era of development began. The Portland Oregonian then predicted that there would follow "tremendous stampedes from California, a flood of overland immigration and vastly increased business on the Columbia." The shrewd forecast of the sagacious editor was fulfilled to the foot of the letter. Of the total yield from the mining districts in northern Idaho it is impossible to secure exact figures. A conservative estimate would put the production from the time of discovery until 1900 at about $50,000,000, of which probably $35,000,000 were obtained before 1870. In this connection Dr. Trimble rightly directs attention to the fact that the mines of eastern Oregon have not yet received the study that their importance as builders of that part of the state would warrant. The mines of the Boise basin in Idaho not only were rich and easily worked, but were so situated as to encourage homemaking and the up-building of a permanent community. Soon towns with stable interests and staple industries arose. The mining founders of Boise showed themselves to be exceptionally enterprising and farsighted men. As the Caribou, British Columbia, mines had shown that in placer fields the individual, once a camp was established, could do little except labor for some one else or in lieu of this prospect for new fields, some form of organized or cooperative effort being essential to the development of mining, even in its simpler stages; so now the War-Eagle quartz-mines of Idaho, remote and newly born, called for outside capital and for science. The mining advance gave occasion for the creation of British Columbia, Idaho and Montana as political units. In considering the societies that owe their origin to mining it is essential to remember that almost from the moment of discovery cooperation is indispensable in the development of gold-fields and also that the individualism of placer-mining frequently is greatly exaggerated. In the period now under review "the lone prospector" was much of a myth. This and similar seemingly small matters are among the many observed by Dr. Trimble's microscopic eye, which also is not wanting in telescopic range, that show how thoroughly he has surveyed his field and with what scrupulous science he has interpreted all his facts.