Geology topics

C.H. Burgess

Publications and source records attributed to C.H. Burgess.

3 recordsLinked to original sources

USGS2014

The igneous rocks of the Highwood Mountains of central Montana

The study of the Highwood Mountains was undertaken by a group of men from Harvard University under a grant from the Shaler Memorial Fund of the Department of Geology. The work was under the general direction of Larsen, who, with the assistance of Norman A. Haskell, mapped most of the volcanic rocks. Hurlbut and Griggs worked mostly on the laccoliths, Burgess on the stocks, and Buie on the dikes. The party spent two summers in the field. The laboratory work is far from complete. We cooperated closely in all the work.

Montana↗

USGS1941

Igneous rocks of the Highwood Mountains, Montana: Part VI. Mineralogy

The minerals of the igneous rocks of the Highwood Mountains are described. The primary hornblende of the quartz latites is basaltic and it has been partly replaced by a common green hornblende. Hornblende is rare in the alkalic rocks. Augite is an abundant mineral of the alkalic rocks; in the syenites it contains some acmite, especially on the borders of the crystals. Aegirite is a common metamorphic mineral. The olivine of the shonkinites contains from 12 to 22 mol per cent of fayalite, that of the syenite from Square Butte 50 per cent. Monticellite twinned into trillings on (031) is an abundant mineral in one small intrusive body. In the alkalic rocks barium sanidine is abundant and plagioclase rare; leucite, primary analcime, and pseudoleucite are common and sodalite rare. Natrolite, thomsonite, and other zeolites are widespread and very abundant.

Montana↗

USGS1941

Igneous rocks of the Highwood Mountains, Montana: Part VII. Petrology

In the shonkinite series olivine, leucite, and analcime crystallized only from magmas with over 20 per cent of mafites. At this stage the leucite and analcime inverted to pseudoleucite. Pyroxene crystallized over the whole range of rocks and changed little in composition until the magma reached the composition of nepheline syenite when it became richer in aegirite. A little pale biotite crystallized early, but most of the biotite is dark and crystallized late. A little barium rich sanidine crystallized early. The abundant late feldspar is poor in barium. Four petrographic subprovinces are represented in the area. The older quartz latites are near lime-alkalic rocks, the syenites and monzonites of Highwood Peak are somewhat farther removed, and the shonkinite series are potash-rich alkalic rocks. The alnoites are very rich in lime. The parent mafic magmas of the various subprovinces formed in depth by differentiation of a primary basaltic magma. These parent magmas were erupted toward the surface and there differentiated in a different way. The differentiation of the shonkinite magma was chiefly by settling of augite, olivine, and some biotite.

Montana↗