. 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. iililii \ ^ A. GEOLOGICAL SURVEY OF THE TERRITOEIES. 51 posed of compact trachyte, but surrounded with stratified breccia orcoDglomerate, jutting up agaiust the sides and reaching nearly or quiteto the summits. Indeed, some of the highest peaks are apparently madeup of the conglomerate. We may conclude, not only that the carvingout of the channel of the Grand Oauon was a very modern event, bu
. 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. iililii \ ^ A. GEOLOGICAL SURVEY OF THE TERRITOEIES. 51 posed of compact trachyte, but surrounded with stratified breccia orcoDglomerate, jutting up agaiust the sides and reaching nearly or quiteto the summits. Indeed, some of the highest peaks are apparently madeup of the conglomerate. We may conclude, not only that the carvingout of the channel of the Grand Oauon was a very modern event, butthat the deposition of the entire material which forms the caiion is, in ageological sense, quite a modern occurrence. Ihe drainage of the countrycommenced long before the excavation of the present water-courses, butit is difficult to answer the question how this great drainage was broughtabout, unless we account for it by a general elevation of the entirecountry, gradually sending this immense body of water, which must haveprevailed all over the ISTorthwest at least, perhaps all over the EockyMountain region, westward into the Pacific and eastward into theAtlantic. As the waters slowly subsided they were separ
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