We have attempted to give, in this bulletin, such information concerning the iron ores of Minnesota as might be wanted by the explorer, the miner, the geologist and the citizen of the state. There has been a great demand recently for such a discussion of the iron ores of the Northwest. As the discovery of new mining grounds has, year after year, extended the interest in iron mining among a greater number of individuals and corporations who naturally look to the official survey for information and guidance, so have the number and complexity of the problems involved increased. We have not essayed the settlement of all the scientific questions that have arisen through this extension of the field of observation. We have simply collected the new facts as we have learned them and have made an initial effort to group all of them, both old and new, under a classification intended to make them indicate some general principles. Our results are not wholly in accord with those of some of our predecessors-as theirs were not with theirs. We would have been glad to have taken more time for further field and laboratory work. It is evident, however, that we should never reach perfection. It was equally evident that justice to a large and expectant constituency required the preparation of a report on the iron ores, however far it might fall short of rendering justice to the subject. It is only through successive partial studies, and the publication of the incompleted results that some additions are made to our knowledge of the geology of the ores of iron. Our contribution to that fund of knowledge will go with others, both earlier and later, to enable some fortunate future geologist to prepare an exposition that will be both thorough and complete. We shall be satisfied if we may be able to add a small quantum to that end.