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A number of years ago I suggested that the ores which have been deposited by hot ascending waters fall naturally in three classes dependent upon the phys!cal conditions surrounding their genesis. 2 Later on, this mode of subdivision was introduced in a textbook on "Mineral Deposits ,,a and it has since been adopted by other authors. 4 It was recognized from the start that the various classes were not sharply defined but gradually merged. On the other hand, the principle of classification seemed the only one suitable for a genetic system. • It was also evident that the classification lacked a concise terminology and critics have not failed to emphasize this. While it seemed inexpedient to introduce new terms until the underlying principle was vindicated, the time for this introduction would seem to have arrived now, if acceptable names can be provided. The general classification outlined in the work referred to has also been subjected to some criticism 5 on account of its alleged lack of strictly logical categories. This criticism may be well founded, but in the present state of our knowledge such a strictly logical system would be quite useless. There must be some elas- .

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SIR: I have the honor to transmit herewith the manuscript of a• report entitled ''A Geological Reconnaissance across the Bitterroot Range and Clearwater Mountains in Montana and Idaho, by Mr. Waldemar Lindgren." The report contains the results of a rapid reconnaissance made in August, September, and •october, 1899, covering an area of 12,000 square miles in Idaho, Montana, a:nd Oregon. The region is one concerning the geology of which little iilformation is available, and this report, while merely a reconnaissance, Rhould be of material assistance in the development of the economic resources of the region.Very respectfully,