2/4 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



the Mono Valley in East California. The magnificent basalt 

 plateau in Oregon and Washington, through which the Columbia 

 River has channeled its course, was made known to the 

 scientific world by Hayden, and the same geologist described 

 for the first time in 1871 the wonderful lava plateau in North- 

 Western Wyoming, on the banks of the Yellowstone River, 

 with geysers, hot springs, mud volcanoes, and extinct volcanic 

 hills. Since the Yellowstone Park became in 1872 the 

 national property of the United States, the Geological Survey 

 Department has carried on without intermission the work of 

 scientific exploration and detailed research in this region. 

 Professor Iddings has described the volcanic rocks of the 

 National Park in two memorable reports of the United States 

 Survey (1888 and 1889). 



Farther south, the high table-lands of Colorado, Arizona, 

 and New Mexico display a number of extinct volcanoes 

 which have broken through horizontal strata of Palaeozoic age 

 and repose upon them as widespread sheets or conical hills. 

 The volcanoes in Southern Colorado and in Arizona were 

 described by Powell, Wheeler, King, Gilbert, and others, and 

 in 1882 the United States Survey published Button's admir- 

 able monograph of the Grand Canon district. 



The Henry mountains, in the greatly denuded region west 

 of the Colorado River, will always be memorable in geology 

 as the locality of Gilbert's epoch-making researches on volcanic 

 rocks. Gilbert demonstrated there the true nature of certain 

 deep-seated intrusions which had made their way mainly along 

 the bedding-planes of sedimentary strata, had solidified there 

 in cistern-like form, and displaced the surrounding beds by 

 their pressure. Such intrusions were termed " laccolites " by 

 Gilbert, and in so far as they exert uplifting forces on the strata 

 above them, Gilbert's laccolitic intrusions are reminiscent of 

 Von Buch's Elevation-Craters. The term of " laccolite," 

 together with Gilbert's explanation, is almost universally 

 accepted by geologists. Peale, Holmes, and Endlich (1877) 

 have shown how, in virtue of denudation and removal of the 

 stratified rock-materia 1 , individual laccolites have been exposed 

 superficially as dome shaped bosses of igneous rock. 



Alexander von Humboldt was the first to explore the 

 Mexican volcanoes, and the German geologists Felix and Lenk 

 published, during the years 1888-91, valuable contributions 

 to the geology and palaeontology of Mexico. The volcanoes 



