Identifier: sixthannualrepor00geol (find matches)
Title: Sixth annual report of the United States geological survey of the Territories, embracing portions of Montana, Idaho, Wyoming, and Utah : being a report of progress of the explorations for the year 1872
Year: 1873 (1870s)
Authors: Geological and Geographical Survey of the Territories (U.S.) Hayden, F. V. (Ferdinand Vandeveer), 1829-1887
Subjects: Botany Zoology Meteorology
Publisher: Washington : G.P.O.
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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n Eange, one above Indian Creek, one at Bear Creek,and a third up Jackass Creek, at the lower end of the valley. AboveIndian Creek I found the ridges and peaks made up of mica-schists,which were so covered with detritus that little could be determined inregard to them. We had a great deal of bad weather about this time,which also interfered much with my work. Among the specimens Iobtained are aplite, micaceous gneiss, and quartz. Bear Creek is asmall stream, joining the Madison on the right side, about forty-eightmiles below the caiion. The rocks at the mouth are hard blue and yel-low limestones, containing fragments of corals and crinoids. These Itake to be either Upi^er Silurian or Devonian. The layers are verymuch contorted, but the dip is about west, or, perhaps, a little north ofwest; angle, 20° to 30°. These beds are followed by dark-blue Carbo-niferous limestones, containing Strophomena, Spirifer, Froductus, andOrthis. 11 G s 162 GEOLOGICAL SURVEY OF THE TERRITORIES. Fig. 41.
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INVERTED BEDS OF JACKASS CREEK. The entire exposure oflimestones is about 800 feetin thickness. The upper,or rather lower, layers—for they are inverted as Ifound them in the middlecanon—are magnesian, andcontain in places bladedcrystals of tremolite. Thelimestones are followed by430 feet of massive quart-zites, which are at firstwhite and then dark fromthe presence of iron. Be-neath the quartzites, anddipping in the same direc-tion at an angle of 20°, arealternate layers of sandyand calcareous shales, withinterlaminated bands ofcoal-like slates, whichbreak readily at right an-gles to the plane of deposi-tion. They are followedby greenish-gray calcare-ous sandstones, breakinginto lamina from ^ inch to2 or 3 inches in thickness.These contain Trigonia, Mo-diola, and other fossils,proving their undoubtedJurassic age. All of theserocks are conformable toeach other. Jackass Creek joins theMadison at the lower endof the valley, just abovethe lower canon. Thiscreek, like the others, cuts

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