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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a. The question arises in the mind, Whence originated this vastdeposit of breccia or conglomerate, and what were the physical condi-tions under which the materials were deposited ? As to their origin, wemust conclude that they were thrown out by volcanoes into the sur-rounding waters much as similar materials are ejected from modernvolcanoes at the present time. We find, however, that these brecciasare of immense thickness, sometimes 4,000 to 5,000 feet, as at the GEOLOGICAL SURVEY OF THE TEREITOEIES. 39 sources of the East Fork and iu the mountains at the head of the UpperYellowstone above the lake. Some of the highest mountains in theNorthwest are capped Axith these volcanic breccias arranged in horizon-tal strata, and showing- most clearly that the agent was water. Inalmost all cases these stratified breccias are perfectly horizontal frombase to summit, thereby indicating the probability that there has beenno important movement of the earths crust since their deposition. We Fig. 4.
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VOLCA>;iC BRFXCIA AT THE HEAD OF CANON AND ROCK CREEKS. must conclude, then, tbat at a comparatively modern date tbe waters socovered these mountain-ranges of the Korthwest that not even the sum-mits of the loftiest peaks were above the surface. It is barely possiblethat we might make an exception in the case of the Grand Tetons. Wemay suppose that the materials were supplied from the numberless vol-canic fissures in unlimited quantities in a comparatively brief space oftim£; but the period which would be required for the waters to arrange 40 GEOLOGICAL SURVEY OF THE TERRITOEIES. this matter in the remarkably uuiform and compact series of strata whichwe find at the present time must have been great. The results havebeen carried on upon such a stupendous scale that the mind finds withdifQculty the courage to grapple with them or attempt to explain them.And then, subsequent to the deposition of these enormous beds of con-glomerates, has been the wearing-out of canons and valleys 2,0

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