Formations, would be stopped abruptly by the less resistant shales above. When the magma reached the shale beds, the weight of the column of igneous rock could have exceeded the strength of the shale, causing the magma to flow horizontally. No indication of horizontal spread, however, is observed. The continuously cylindrical shape of the intrusions indicates that the magma moved steadily upward and probably reached the surface. 10. Carbonatites have been found, and formally reported, in the nearby Bear Lodge Mountains, and also as fragments in the alloclastic breccias of the Missouri Buttes. Their presence suggest a high volatile content for the magma and the possibility of explosive volcanism.” [Illustration: 1.] [Illustration: 2.] [Illustration: 3.] SELECTED BIBLIOGRAPHY Carpenter, F. R., 1888, Notes on the geology of the Black Hills: Preliminary report of the South Dakota School of Mines, Rapid City, S. Dak. Darton, N. H., 1909, Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming: U. S. Geol. Survey Prof. Paper 65. Darton, N. H., and O’Harra, C. C., 1907, Description of the Devils Tower quadrangle, Wyoming: U. S. Geol. Survey Geol. Atlas, folio 150. Dutton, C. E., and Schwartz, G. M., 1936, Notes on the Jointing of the Devil’s Tower, Wyoming: Jour. Geology, v. 44, no. 6, p. 717-728. Imlay, R. W., 1947, Marine Jurassic of the Black Hills area, South Dakota and Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 31, no. 2, p. 227-273. Jaggar, T. A., Jr., 1901, Laccoliths of the Black Hills: U. S. Geol. Survey 21st Ann. Report, pt. 3, p. 163-290. Pirsson, L. V., 1894, On some phonolite rocks from the Black Hills: Am. Jour. Sci., 3d ser., v. 47, p. 341-346. Zuidema, H. P., 1948, The touring public discovers Mato Tipi (Devils Tower, Wyo.): Earth Science Digest, v. 3, no. 1, p. 3-7. Halverson, D. L., 1980, Geology and petrology of the Devils Tower, Missouri Buttes and Barlow Canyon Area, Crook County Wyoming, Dissertation. Transcriber’s Notes —Publication information is from the original print copy—this e-text is public domain in the country of publication. —Silently corrected palpable typos; left non-standard spellings and dialect unchanged. —Split single captions describing multiple images, into multiple captions. —In the text versions, delimited italics text in _underscores_ (the HTML version reproduces the font form of the printed book.) End of the Project Gutenberg EBook of Geology of Devils Tower National Monument, Wyoming, by Charles S. Robinson