554 



SCIENCE 



[N. S. Vol. XXXIII. No. 850 



study of the region under the auspices of 

 the United States Geological Survey, I 

 published in official documents, and later 

 in Johnson's "Universal Cyclopsedia, " an 

 article entitled "Thermal Springs," in 

 which I stated the conclusion that the 

 waters of these hot springs and geysers 

 were essentially meteoric waters that had 

 penetrated downwards a sufficient distance 

 to attain an increased temperature, only to 

 be forced again to the surface by ascend- 

 ing currents. 



I propose on this occasion to present 

 briefly some of the geological evidence on 

 which these conclusions are founded. They 

 are based on the nature and structure of 

 the rocks through which the heated waters 

 reach the surface, the mineral constituents 

 contained in the waters, the composition of 

 the associated gases, and the characters of 

 the varied sediments and incrustations de- 

 posited around the springs and pools. 



EOCENE IGNEOUS ROCKS 



To understand correctly the relations of 

 the thermal waters found in the park to 

 existing geological conditions, a brief his- 

 tory of the salient features of its igneous 

 rocks and their sequence seems necessary. 

 The country included within the Yellow- 

 stone Park, the Absaroka Range, and the 

 Wind River Plateau, consists essentially of 

 masses of igneous rocks covering an area 

 of over 5,000 square miles in the center 

 of a continent whose three great rivers, the 

 Mississippi, the Colorado, and the Co- 

 lumbia, here find their source. Within this 

 region, through that vast period of time 

 from the close of the Archsean to the dawn 

 of the Tertiary, all evidences of eruptive 

 energy are wanting. Coincident with the 

 earliest indications of the post-Laramie 

 orogenic movement came a period of in- 

 trusion which began in late Cretaceous 

 time and continued with only slight pe- 



riods of rest till near the end of the Pliocene. 

 Whatever the primary causes were that 

 produced this orogenic movement, the en- 

 largement of the continental area, and the 

 final withdrawal of the sea, they brought 

 about mountain uplifts, crustal displace- 

 ments, and volcanic activities of the first 

 magnitude. The close of the Cretaceous in 

 this part of the northern Cordillera was 

 marked by the most profound stratigraphic 

 break since Algonkian time. The oldest 

 intrusives, recognized as such, are found in 

 the northwestern corner of the Yellowstone 

 park in what is now the Gallatin Range, 

 and inaugurated a physical revolution. 

 These rocks were forced in as sills between 

 upper Mesozoic sandstones before the latter 

 were much disturbed, as they lie uncon- 

 formably interbedded between sediments 

 which later were affected by the dynamic 

 processes of mountain elevation. In this 

 sense these earliest intrusions must be con- 

 sidered, structurally at least, as of Creta- 

 ceous age. They were succeeded by more 

 powerful injections, accompanied by slow 

 and protracted elevation of the Gallatin 

 Range. With the emergence of land sur- 

 faces erosion followed and sediments were 

 deposited unconformably. Elevation of 

 mountain masses produced new physio- 

 graphic features, and as a consequence 

 changes in climatic conditions and modifi- 

 cations of living species, both animal and 

 vegetable. The Tertiary period was 

 ushered in. With the progressive building 

 up of the range and the associated folding 

 and compression of strata, viscous magmas 

 were injected from unknown depths. Mas- 

 sive bodies were forced upward to definite 

 levels, when, being unable to rise higher, 

 they spread out laterally between strata of 

 all ages from the Cambrian to the Laramie. 

 Centers of powerful intrusion shifted from 

 one locality to another, and within the con- 

 fined limits of the range batholiths of no 



