March 24, 1899. J 



SCIENCE. 



441 



sure the material was squeezed upward to 

 higher levels, following lines of least resist- 

 ance, and consolidated at greater or less 

 depths beneath the surface. This upward 

 movement was probably coincident with the 

 crustal movements that elevated the entire 

 Absaroka Range. 'The line of Ishawooa 

 intrusives marks the trend of one such up- 

 ward movement of molten magma, which 

 for the most part congealed without finding 

 egress to the surface. That a portion of 

 the magma may have been pushed uj)ward 

 through fissures and vents and discharged 

 as surface flows of andesite is possible, but 

 of such flows, if they existed, no positive 

 evidence remains. 



Conditions somewhat similar to those 

 found in the Absarokas are described by Pro- 

 fessor Adolph Stelzner as occurring in the 

 Andes of Argentina. He describes granites, 

 diorties and syenites as penetrating the 

 andesitic tuff's and lavas of Tertiary age, and 

 as cooling under a heavy load of superim- 

 posed material. He does not regard these 

 massive crystalline bodies as conduits of vol- 

 canoes, but as large stocks formed independ- 

 ently of such vents. He refers to them as 

 taking part in the great orogenic uplift which 

 elevated the Cordillera of South America, 

 an uplift which began in Jurassic time, 

 lasted through the Mesozoic, and continued 

 through the greater part of the Tertiary. 



In the discussions of volcanic phenomena 

 found throughout geological literature, cir- 

 cular vents of great depth seem to be re- 

 garded as indispensable and are supposed to 

 furnish an open door for the molten mag- 

 mas, permitting them to take a straight 

 shoot from the eternal depths to daylight. 

 In this way geologists certainly avoid many 

 perplexing physical problems which con- 

 front us in the case of stocks and laccoliths 

 penetrating sedimentary rocks and stopping 

 far short of the siirface. In speaking of 

 areas of igneous rocks, one almost hesitates 

 to use the term laccoliths, so universally is 



it referred to in its relation to sedimentary 

 rocks. For my part, it seems far more 

 reasonable to look for such intrusive bodies 

 in areas of igneous rock than in regions of 

 sedimentation. That large intrusive bodies 

 came to a standstill without any surficial 

 manifestations, in the Absarokas, is, I 

 think, fairly well determined. 



Two years ago it was my good fortune to 

 cross the Cascade Range at a number of 

 localities and to climb far above timber line 

 the slopes of Mount Rainier, in "Washing- 

 ton ; Mount Hood, in Oregon, and Mount 

 Shasta, in California. From these com- 

 manding points comprehensive panoramic 

 views were obtained over a broad field of 

 igneous rock. Majestic and impressive as 

 are these volcanoes, and grand in their iso- 

 lation, I could but feel that back of them 

 all lay earlier chapters in the Tertiary his- 

 tory of volcanic energy on the Pacific side 

 of the Cordillera ; that these powerful vol- 

 canoes were but a late expression of the 

 intensity of the eruptive energy, and that 

 still earlier volcanic masses had in some 

 way taken part in the orogenic disturbances 

 of an earlier Tertiary time. So, on the 

 east side of the great Cordillera, the early 

 Tertiary fires long since ceased to glow in 

 the Absarokas, and the center of volcanic 

 energy moved westward and built up on 

 different lines the broad rhyolite plateau of 

 the Yellowstone Park, a plateau strongly 

 contrasted with the Absarokas in the al- 

 most^ entire absence of breccias. The work 

 of such investigators as Emmons and Cross 

 in Colorado and Weed and Pirsson in Mon- 

 tana is slowly but surely solving the prob- 

 lems of the post- Cretaceous uplift in the 

 northern Cordillera, and, it will, I think, 

 finally be shown that the crystalline rocks 

 consolidated below the surface have played 

 an important part in bringing about the 

 Cordilleran revolution. 



On a bright crisp autumnal day in 1897 

 I left the Absarokas by the way of that 



