The Belt series in Montana, with a geologic map and a section on paleontologic criteria

Problems related to the Belt series have been discussed for nearly a hundred years, but the amount of detailed mapping and other quantitative data available, even now, is not commensurate with the importance of the problem.  The present paper is an attempt to summarize existing data in the light of recent fieldwork by the writer and his associates.  While the report deals mainly with the rocks in Montana, where the series was first recognized, it necessarily includes consideration of the series in Idaho and parts of Canada as well as of related rocks in more distant areas.