288 THE JOURNAL OF GEOLOGY. 



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. XL, 

 p. 171, 1877) has suggested that an ice-age is indicated by these 

 events. 



This Rocky Mountain revolution marks the period of the sec- 

 ond 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 forma- 

 tions conspicuously developed on both sides of the British Chan- 

 nel. 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 out- 

 flows 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 



