Geology and Ore Deposits of the Philipsburg Quadrangle, Montana. W. H. Emmons , F. C. Calkins

1918 The Journal of geology  
Prof. Paper 78, 1915. Pp. 271, pls. 17, figs. 55. The Philipsburg quadrangle includes an area of 827 square miles lying immediately west and northwest of Anaconda, Montana. It is a country of strong relief, almost midway between the eastern and western divisions of the Rocky Mountains. The geologic section includes formations ranging in age from Algonkian to Recent. The Belt series, the oldest rocks in the area, is divided on lithologic grounds into six formations. Their total thickness is
more » ... l thickness is 15,000 feet. Next above and separated from the Belt series by a striking unconformity is the Cambrian system, comprising the Flathead, Silver Hill, Hasmark, and Red Lion formations. The Red Lion contains Upper Cambrian fossils. It is overlain by the Maywood formation, of doubtful Silurian age. The Devonian is represented only by the Jefferson limestone; the Mississippian by the Madison limestone; the Pennsylvanian by the Quadrant formation. Though the stratigraphic relations of the Paleozoic systems was not clearly made out, each is probably set off by disconformities. The Mesozoic is not strongly developed in this part of Montana. Only three formations are here present-the Ellis, Kootenai, and Colorado. The early Tertiary was marked by powerful crustal movements. The pre-Tertiary sediments were complexly folded and overthrust and extensive igneous masses were intruded. Later the region was the scene of two epochs of vulcanism. Certain gravel deposits contain Miocene vertebrates. The Tertiary closed with tilting and a general uplift. During Pleistocene time there were at least two stages of Alpine glaciation. The early Tertiary batholiths and smaller intrusives are granites, granodiorites, and diorites, with associated pegmatites, aplites, and lamprophyres. At and near their contacts with these intrusives the sediments are notably altered. The pneumatolytic solutions that effected these changes are believed to have carried chlorine, fluorine, 19l This content downloaded from 165.193.178.102 on July 25, 2016 11:52:44 AM All use subject to University of Chicago Press Terms and Conditions (http://www.journals.uchicago.edu/t-and-c).
doi:10.1086/622582 fatcat:45f6fjmp65bt7dnmn4qtwbzs4m