A. SANDSTONE AT TOP OF RIDGE IN BEARPAW SHALE NEAR SECTION LINE BETWEEN SECS. 33 AND 34, T. 2 N., R. 21 E., MONT. B. BASAL PORTION OF RIDGE-FORMING SANDSTONE IN BEARPAW SHALE NEAR MIDDLE OF SEC. 35, T. 2 N., R. 21 E., MONT. 1 5 Sandstone, yellowish, hard; contains plant remains. Sandstone like that below but without concretions... 17 13 20 318 10 30, T. 2 N., Near the center One of the most prominent ridges extends from sec. R. 21 E., southeastward to sec. 10, T. 1 N., R. 22 E. of sec. 35, T. 2 N., R. 21 E., about 86 feet of rather soft light-yellow massive sandstone is exposed beneath a thin cap of hard reddishbrown, somewhat tuffaceous sandstone. The lower 50 feet of the sandstone is characterized by the absence of bedding and the presence of large reddish-brown concretionary masses, the appearance of which is shown in Plate XX, A and B. The capping sandstone of this ridge dips west at a very small angle beneath the flat area underlain by shale and the more recent alluvial deposits. One of these peculiar sandstones of the Bearpaw caps the long ridge whose east end is known as Gray Hill, in sec. 20, T. 2 N., R. 22 E. A well at the house a short distance southwest, about 30 feet below the capping sandstone, is reported to have penetrated about 120 feet of almost continuous sandstones. The uppermost beds in the stratigraphic section of the Judith River formation measured 14 miles south of Acton and given on page 118 are overlain by about 150 feet of dark-gray shale containing thin layers of sandstone. It is believed that careful search would reveal marine fossils in this shale and that it marks the influx of marine waters, although the shale is overlain by 85 feet of almost pure sandstones that dip steeply eastward beneath the great body of marine shale occupying the valley down which the main Acton-Billings road passes. Owing to the very peculiar development of fresh-water and brackish-water sandstones in the Bearpaw shale it has been thought best to show in the following lists not only the different species of marine fossils that were obtained from the Bearpaw formation but also the exact locality where each collection was obtained. NW. sec. 5, T. 2 N., R. 19 E., in sandy shale about 106 feet below the top of the Bearpaw formation: . Ostrea pellucida Meek and Hayden? Inoceramus sagensis Owen. Nucula cancellata Meek and Hayden. Thracia subgracilis Whitfield. Scaphites nodosus var. plenus Meek and Hayden. SE. sec. 32, T. 3 N., R. 19 E., in beds from 100 to 150 feet below the top of the Bearpaw shale: Baculites compressus Say. Side of main wagon road on section line between secs. 13 and 24, T. 3 N., R. 19 E.: Avicula linguaeformis Evans and Shumard. NW. sec. 27, T. 1 N., R. 21 E., in the shale shown in the stratigraphic section measured north of Antelope Point (p. 122): Leda scitula Meek and Hayden. Lucina sp. Mactra gracilis Meek and Hayden. Dentalium sp. Lunatia sp. Baculites compressus Say. West line of sec. 34, T. 1 N., R. 21 E., on the shale slope below the prominent bench of sandstone south of Antelope Point: Ostrea sp. Baculites compressus Say. Portions of the vertebra of a large plesiosaur. In general the Bearpaw formation occupies a low-lying area between the slightly elevated portion of the field underlain by the older rocks and the escarpment formed by the overlying Lennep sandstone. It occupies the greater part of Lake Basin and a long, narrow belt extending from Broadview southeast to Huntley LENNEP SANDSTONE. The name Lennep sandstone was adopted by Stone and Calvert1 for a group of andesitic beds which lie stratigraphically between the Bearpaw shale and the Lance formation along the north flank of the Crazy Mountains. Lennep, from which the formation takes its name, is a station on the Chicago, Milwaukee & St. Paul Railway at the north end of the Crazy Mountains, in the immediate vicinity of a ridge formed by these beds. In the type locality the Lennep sandstone is composed of dark-colored tuffaceous sandstone intercalated with dark shale, and at several places near the middle a band of 1 Stone, R. W., and Calvert, W. R., Stratigraphic relations of the Livingston formation of Montana Econ. Geology, vol. 5, p. 746, 1910. brown nodules 8 to 12 inches in diameter was observed. It occupies the approximate stratigraphic position of the Fox Hills sandstone, but its lithology is different and it lacks the characteristic Fox Hills fauna. It is transitional from the marine Cretaceous to the freshwater "Ceratops beds" (Lance formation). There is a very rapid thinning and also a marked change in the character of the Lennep formation from west to east across the Lake Basin field. In sec. 28, T. 4 N., R. 18 E., it can be readily separated into three belts. The lower belt consists of about 35 feet of massive light-colored and in places false-bedded sandstone. This belt is overlain by one of light yellowish-brown andesitic rock, and this in turn by an upper rim of very tuffaceous material. A thin coal bed was observed a short distance above the lower light-colored sandstone near the coulee south of the house in sec. 30, T. 4 N., R. 18 E., in secs. 34 and 36, T. 4 N., R. 18 E., and in secs. 4 and 5, T. 3 N., R. 19 E. The details of the Lennep formation in the northwestern part of the field are shown in the following stratigraphic section: Section of the Lennep sandstone in sec. 29, T. 4 N., R. 18 E. Tuff, dark colored, hard, underlying Lance beds.... Ft. in. 1 4 Tuff, dark, thin bedded; weathers out, leaving dark concre Sandstone, fairly massive and light colored, irregularly bedded. 14 8 Tuff, yellow, more resistant than the bed above; forms a ledge. 6 25 the Lennep ridge....... Tuff, hard, in places very massive; commonly forms the top of Tuff, fairly soft, sandy; contains bone fragments.. 16 48 6 Sandstone, hard...... 8 Shale, yellowish, sandy; contains some andesitic material.... 27 3 Sandstone, gray, massive bedding, extremely irregular; shows |