File: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 (1901) (14784204362).jpg

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:
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Contributing Library: Clemson University Libraries
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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he north, northeast, southeast, and south, v^ery near the porphyry.In all cases the bedding appears undisturbed by the eruptives, and hasa slight westerh dip. The four buttes arc all composed of porphyry.The rock on the summit is frequently fused at the edges of jointblocks to buff porcelaneous material, probably fulgurite produced bylightning. The Warren Peaks from this summit are more impressivethan when seen from lower levels—culminating long slopes which risegently on both sides. Far to the northward the snowy summits of theBighorn Range may be descried. Granite fragments were included inthe porph3ry mass of the western butte, similar to those found in thebreccia at the base of the buttes. The northeastern peak shows somecolumnar structure, with almost horizontal columns, the pentagonalcolunui ends projecting from the face of the rock. There are alsoledges trending north and south which stand out like dikes in theclefts of the rock mass, but they show no evidence of being litho-
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JAGGAR.) LITTLE MISSOURI BUTTES. 257 logically different. The spur extending southward from the foot ofthis peak is covered with rounded bowlders of coarse granite, trap,sandstone, and pegmatite, though none of these occur in the rockytakis above, at the foot of the porphyry wall; evidently the breccialies under the porphyry. The Little Missouri Buttes are four in number, the two northernones being the highest and the most smoothly rounded in form. Theyare arranged at the corners of a quadrilateral, from one-half to three-quarters of a mile apart, and the porphyry is apparently continuousthrough the whole group except on the eastern side, where a streamhas cut a canyon through it into the soft agglomerate that underlies it.This agglomerate occurs within the area of the Buttes on both sides ofthis stream and south of the southeastern butte. The talus slopes markthe contact between agglomerate and phonolite. Fifty feet abovethe gulch between the two eastern buttes occurs buff sandstone

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