Petrographic province of Central Montana

Igneous rocks and related mineral deposits of the Barker Quadrangle, Little Belt Mountains, Montana

“…The rocks that form the various intrusions belong to the Little Belt subprovince, one of Larsen's (1940) divisions of the central Montana petrographic province. In the Peacock (1931) ( 1) those that were likely formed before most of the major intrusions were emplacedold felsic rocks, and (2) those that were formed after the large intrusions-young felsic rocks.…”

Rocks and mineral resources of the Wolf Creek area, Lewis and Clark and Cascade counties, Montana

“…« The rocks of Adel Mountain Volcanics are similar in chemical and mineral composition to volcanic rocks of early Eocene age in the Absaroka Range east of Yellowstone National Park in northwestern Wyoming, and, in addition, they are not unlike some of the alkalic volcanic rocks of Eocene age in the High wood and Bearpaw Mountains in the plains region of central Montana (Larsen, 1940, p. 907;Lyons, 1944, p. 470). The volcanic rocks of the Absaroka, Highwood Mountains, and Bearpaw Mountains belong to the Tertiary alkalic petrographic province of central Montana as defined by Larsen (1940). This chemical affinity does not, of course, provide a firm basis for correlation.…”

The Cenozoic rocks; a discussion to accompany the geologic map of the United States

“…These are mostly near-surface stocks and laccoliths, and in some of the areas, notably the Highwood and Bearpaw Mountains, effusive equivalents are preserved. The igneous rocks range in composition from ordinary rhyolites, andesites,and syenites, to strongly alkalic rocks rich in potash and soda (Larsen, 1940). The igneous rocks east of the Rocky Mountains are generally credited to be of Eocene age.…”

“…is reported from it. Another somewhat smaller body of quartz monzonite, nearly surrounded by Cretaceous plutonic rocks, forms the Sawtooth Range farther southwest (Reid, 1963, p. 14 (Larsen, 1940). In a few places, effusive equivalents are preserved.…”