The U.S. Geological Survey has recently measured and sampled the Phosphoria formation at many localities in Montana and other western states. These data will not be fully synthesized and analyzed for several years, but segments of the data, accompanied by little or no interpretation, are published as preliminary reports as they are assembled. This report, which contains abstracts of many of the sections in southwestern Montana (fig. 1), is one of this series and is the fourth Montana report; it includes the second half of the data gathered in Montana during 1949 and 1950. The field and laboratory procedures adopted in these investigations are described rather fully in a previous report (McKelvey and others, 1953).
Many people have taken part in this investigation. The program of which this work is a part was organized by V. E. McKelvey. J. L. Elliott, W. J. Garmoe, R. F. Gosman, C. W. Tandy, and W. H. Wilson participated in the description of strata and the collection of samples referred to in this report. Crushing and splitting of the samples in the field was done by T. K. Rigby. The laboratory preparation of samples for chemical analysis was done in Denver, Colo., under the direction of W. P. Huleatt.
