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SCIENCE. 



[N. S. Vol. IX. No. 221. 



miles, represents a continuous ridge, the 

 result of the consolidation of a molten 

 magma intruded into the breccias. Erosion 

 has as yet laid bare only the more elevated 

 portions and some of the connecting links. 



If a trained geologist were to stand on 

 any one of the more prominent points in the 

 Absarokas his attention would, first of all, 

 be attracted by the vast amount of frag- 

 mental ejectamenta lying with apparent 

 horizontality in every direction. Closer 

 observation would impress him with the 

 bedded nature of much of this material and 

 the action which running water had played 

 in disintegrating the lava and rounding the 

 andesitic and basaltic bowlders. If, by 

 chance, he had acquainted himself with the 

 huge stocks exposed in the canyons, know- 

 ing the power of dense crystalline rocks to 

 withstand atmospheric agencies better than 

 the easily disintegrating breccias, he would 

 be surprised to find that none of the larger 

 ones towered above the plateau in com- 

 manding peaks. At one or two localities 

 they attain the present level of the plateau, 

 but do not rise much above it, and usually 

 give evidence of the dying out of the energy 

 which forced the magma upward. As these 

 intrusive stocks are overlain by breccia 

 sometimes 1,000 feet in thickness, it is diffi- 

 cult to see how they ever could have been 

 centers of powerful extrusive eruption. 



In an address delivered before the British 

 Association for the Advancement of Science 

 in September, 1893, Professor Iddings took 

 the ground that the Crandall Basin stock 

 was the core of a grand volcano, from 

 which issued the breccias, silts and tufifs 

 which have built up the north end of the 

 range, while the gabbros and diorites repre- 

 sent the coarsely crystalline development of 

 that portion of the magma which cooled at 

 great depths beneath the sui-face. He re- 

 constructed a volcano to a height of 10,000 

 feet above the plateau, and subsequently re- 

 moved by erosion every vestige of the 



volcano down to the summit of Hurricane 

 Mesa, the present level of the plateau. He 

 likens it, iu magnitude and in the processes 

 by which it was built up, to the volcanoes 

 of yEtna and Vesuvius. An abstract of the 

 address was- published in the Journal of 

 Geology for September and October, 1893, 

 and in a forthcoming report on the geology 

 of the Yellowstone National Park a detailed 

 description of the Crandall stock will be 

 found, together with the results of his ad- 

 mirable petrographic studies of the rocks, 

 to which allusion has already been made. 

 After what has been said, it seems hardly 

 necessary to add that with these geological 

 views of Professor Iddlings I do not agree. 

 My interpretation of the history of this re- 

 gion may possibly call forth the friendly 

 criticism that this address is an account of 

 the early Tertiary volcanoes of the Ab- 

 sarokas with the volcanoes left out. For 

 such criticism there may be some slight 

 ground ; but, while I fail to see any evi- 

 dence of the building-up of such volcanic 

 piles as Vesuvius and ^tna, or, as I should 

 prefer to put it, volcanoes of the type of 

 Kainier, Hood or Shasta, there was dis- 

 played intense explosive energy accom- 

 panied by immense volumes of steam and 

 the piling-up of a vast block of lavas from 

 many centers of activity . Instances of such 

 explosive energy may be seen at Chaos 

 Mountain, but the material thrown out 

 yielded readily to atmospheric agencies and 

 soon became spread out over the entire re- 

 gion. The whole area of the late acid brec- 

 cia suggests several powerful vents for the 

 ejectment of fragmental material and the 

 partial wearing- away of mounds and ridges 

 of the heaped-up accumulations. It is pos- 

 sible that before the Sunlight and Ishawooa 

 intrusives were forced upward volcanoes 

 existed, but that any one or two of them 

 dominated the region and influenced the 

 topographical configuration of the Absaro- 

 kas is exceedingly doubtful. There is noth- 



