No abstract

Sandstone: hard, pale, yellowish-orange, thick-bedded Chert: hard, light-gray, thick-bedded chert interbedded with medium-hard, pale yellowish-orange, thick-bedded chert Sandstone and chert: medium-hard, light-gray, thick-bedded sandstone containing some iaterbeds of hard, light-gray chert 31 Sandstone and chert: medium-hard, brownish-gray, thick-bedded sandstone interbedded with hard, light-gray, thick-bedded chert 14 Sandstone: medium-hard, yellowish-brown, thick-bedded sandstone interbedded with hard, brownish-gray sandstone 10 Chert: medium-hard, dusky yellowish-orange, to medium-brown, thick-bedded Mudstone: medium-hard, light-gray to yellowish-brown, thick-bedded Sandstone: hard, light-gray to yellowish-brown, thick-bedded; lowermost 0.75 foot phosphatic 19 12 Member D Mudstone: phosphatic, soft, brownish-black, thin-bedded 15 Mndstone: soft, brownish-black to black, fissile 150 2OO 250 3OO 25 Phosphate rock: oolitic, soft, dark-brown, thin-bedded 22 14 Phosphate rock and mods too*: oolitic, medium-hard, brownish-gray, phosphate rock, interbedded with medium-hard, brownish-gray mudstone 12 Member C Sandstone: soft, dusky yellowish-orange, thick-bedded 41 Sandstone and chert: medium-hard, light brownish-grsy, massive sandstone interbedded with hard, yellowish-gray, massive chert 45 Dolomite: sandy, medium-hard, medium-to light-gray; contains lenses and nodules of chert Sandstone: soft, dusky yellow, thin-bedded; contains many lenses and nodules of chert 35 Chert: hard, medium-grny to yellowish-brown, thick-bedded; contains some interbeds of mudstone and sandstone Member B Mud atone: medium-hard, medium yellowish-brown, thin-bedded; contains several small lenses of oolitic phosphate rode 14 Phosphate rock and mudstone: soft, brownish-gray, oolitic phosphate rock interbedded with soft, pale yellowish-brown mudstone 20 Mudstone: medium-hard, medium yellowish-brown, thin-bedded Member A Mudstone: dolomitic, soft, light-gray, thin-bedded 349 10 Dolomite: medium-hard, pale yellowish-orange, thin-bedded; contains some interbedded cherty mudstone Quadrant formation Sandstone: medium-hard, light-gray, thin-bedded Figure 1. Generalized section of Phosphoria formation at Sheep Creek, Montana

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, will be published as preliminary reports as they are assembled. This report, which contains abstracts of many of the sections measured in southwesterp Montana (pl. 1), is one of this series. The field and laboratory procedures adopted in these investigations are described rather fully in a companion report {McKelvey and others, 1952). Many people have taken part in this investigation. The program of which this work is a part was .organized by V. E.