THE DISSECTED VOLCANO OF CRANDALL BASIN, 



WYOMING.* 



The writer in exploring the north-eastern corner of the 

 Yellowstone National Park and the country east of it came 

 upon evidences of a great volcano, which had been eroded in 

 such a manner as to expose the geological structure of its basal 

 portion. 



The work was carried on as a part of the survey of this 

 region, under the charge of Mr. Arnold Hague of the U. S. 

 Geological Survey. The paper is an extract from a chapter in 

 the final report on the Yellowstone National Park in process of 

 completion, and the writer is indebted to Major J. W. Powell, 

 Director of the Survey, and to Mr. Hague, chief of the division, 

 for permission to present it at this time in anticipation of the 

 publication of the final report. 



The area of volcanic rocks described is but a small portion 

 of the great belt of igneous material that forms the mountains of 

 the Absaroka range, lying along the eastern margin of the 

 Yellowstone Park. 



The volcano of Crandall Basin is one of a chain of volcanic 

 centers situated along the northern and eastern border of the 

 Yellowstone Park, which are all distinguished by a greater or 

 less development of radiating dikes, and by a crystalline core 

 eroded to a variable extent. 



The Palaeozoic and Mesozoic strata, which formed an almost 

 continuous series to the coal-bearing Laramie, had been greatly 

 disturbed and almost completely eroded in places before the 

 volcanic ejectamenta in this vicinity were thrown upon them. 

 The period of their eruption is, therefore, post-Laramie, presum- 

 ably early Tertiary. 



The first eruptions of andesite were followed by those of 

 basalt in great amounts, and these by others of andesite and 



♦Abstract of a paper read before the British Association for the Advancement of 

 Science, September, 1893. 



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