The preparation of a text-book Of Mineralogy was undertaken in 1868, by Prof. J. D. Dana, immediately after the publication of the fifth edition of the System of Mineralogy. The state of his health, however, early compelled him to relinquish the work, and he was not able subsequently to resume it. Finally, after the lapse of seven years, the editorship of the volume was placed in the hands of the writer, who has endeavored to carry out the original plan. The work is intended to meet the requirements of class instruction. With this end in view the Descriptive part has been made subordinate to the more important subjects embraced under Physical Mineralogy.