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ward to the Himalayas, and to the islands beyond, took place chronologically at the same general period, and that this series of disturbances may have affected the whole of the northern hemisphere is further suggested by the occurrence of gigantic erratic blocks of granite in the midst of Eocene strata in the neighborhood of Vienna and other places. Vezien (Rev. Sci. XI., p. 171, 1877) has suggested that an ice-age is indicated by these events.
This Rocky Mountain revolution marks the period of the second great break in the life of the geological ages. The Mesozoic time began with the close of the Appalachian revolution, and closed with the elevation of the Cretaceous beds above ocean-level. In our classification the division line between the Cretaceous and Tertiary was arbitrarily placed at the top of the chalk formations conspicuously developed on both sides of the British Channel. The difficulty American geologists have had in drawing the precise line to separate the Mesozoic from the Cenozoic has resulted from the change of the character of life in the beds in the western interior from marine to brackish, fresh-water and land types. This change was incident to the Rocky Mountain revolution, which had already begun, and was slowly lifting the whole region while the Laramie sediments were being laid down. Several stages may be marked in this grand revolution, but the facts connected with them are not so well-developed as to serve for general purposes of classification of the time scale.
At the close of the Miocene, a great outflow of lava in the northwestern part of the United States took place, and continued with interruptions through the Tertiary into the Quaternary time. About the Columbia River, where it cuts through the Cascade range, the basalt is over three thousand feet thick, and the outflows cover a vast extent of territory, estimated at 150,000 square miles. This was incident to the vast earth disturbance which raised to the amount of at least five thousand feet a large part of the western half of the continent.
There was, still later, a revolution which has left little record in the way of disturbance or discordance of strata, but was of