Identifier: annualreportsofd003unit (find matches)
Title: Annual Reports of the Department of the Interior for the Fiscal Year Ended June 30, 1900--Twenty-First Annual Report of the United States Geological Society
Year: 1901 (1900s)
Authors: United States Department of the Interior
Subjects:
Publisher:
Contributing Library: Clemson University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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it is proliable that the tower represents nearly th(> center ofthe original lens. The massive base bears the same relation to the columns as themedial portion of the dikes flgured in PI. XXXIII. Were it exactlythe equivalent of the dike, we should expect other columns below, themassive portion being in the middle. It is probable that the presenceof a muddy breccia as a lowest stratum for the laccolith interferedwith the development of basal columns, and probably also the actionof gravitation makes the contraction expend itself less symmetricall,yin a horizontal lens than in an upright dike. The present upper sur-face of Mato Teepee is smooth and possibly represents nearly the actualupper contact, from which the shales have been weathered away. The geologic section (PI. XXXVIII) shows an ideal reconstruction Mmld has figured a sill of basalt in Skye, which breaks downward across strata after spreadingalong a higher horizon. Volcanoes; Internal. Sei. Series, Appleton, 1881, fig. .iB.
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JAOGAR.) MATO TEEPEK. 285 of the original laccolithic masses. Mato Teepee was simply a sill orsubordinate lens from the Little Missouri Buttes laccolith. Theencircling drainage favors the hypothesis that the Mato Teepee masswas lenticular, so that streams became adjusted about the peripheralslopes. Po-ssibl) the conduits of Little Missouri Buttes were inclinedto the east from the vertical, so as to inject the magma in the directionof Mato Teepee. The injection was thus eastward, toward WarrenPeaks—i. e., in the same direction as those which formed the Sun-dance Hills, on the opposite side of the Bearlodge Range. Injectedsoutheast through beds gently dipping awav from Warren Peaks, thespreading igneous rock, as usual, truncated bedding planes obliqueh,so that the tirst injections charged with brecciated material reached theMato Teepee region at a horizon lower than that of the conduit. Thesoft breccia probably had its greatest development in the region betweenMato Teepee and the Litt

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