ENBLicH.] COMPARISON OF EEUPTIVES. 261 



basalt, with some scoriae and cinders." .... " The steam and hot ^ases 

 escape from hundreds of vents, and often with considerable noise." 



Another very prominent mountain of the northwestern corner of the 

 United States has been found to show similar conditions. An ascent of 

 Mount Rainier, which is nearly 14,500 feet above sea-level, was accom- 

 plished by A. D. Wilson and S. F. Emmons in 1870. In a paper read 

 by Mr. Emmons, in February, 1877, he describes the ascent.* It was 

 found that the summit of this peak was formed by an ancient crater- 

 rim, and that on the interior rim there were numerous hot jets of steam 

 issuing from under the snow. 



Many other instances of this kind might be mentioned, but these will 

 suffice to show the almost imperceptible connection between the rigid 

 basalts and others, indicating dormant volcanic activity. These latter 

 are gradually dying out, and within, perhaps, a few centuries no hot 

 jets or gases will any longer mark the spots where now we find the last 

 lingering remnants of a former volcanic activity. 



Following northward, parallel with the extensions of the coast-ranges, 

 not within the Rocky Mountains, we reach still active volcanoes. In the 

 Alaskan Range a number of them are located.t 



It is almost an impossibility to draw the line between what might 

 properly be termed basalt, and what must be regarded as still partly 

 active volcanic material. I am not prepared to restrict the occurrence 

 of basalt to a period not prior to the Tertiary, and have no objection to 

 leave the younger line of boundary equally ample. Ootta contends J that 

 no bowlders of true basalt or trachyte have ever been found in Europe 

 in Pre-Tertiary conglomeritic deposits. This would argue an inference 

 directly in opposition to the view of Gieke, which has been given above. 

 From the observations made on the Sweetwater River, in Wyoming, I 

 cannot arrive at any other conclusion than that basalt existed as such 

 before the advent of the Tertiary period. 



In connection with the basalts, I wish to mention the occurrence of a 

 rock discovered in the Green River Basin. In want of a better name, I 

 shall apply that of "leucitophyrite." The leucitophyrs of Italy differ 

 somewhat from that observed in the Green River Basin. Emmons states § 

 that the rock is composed of alight gray to greenish porous paste, with 

 some mica. Under the microscope the entire rock is resolved into leu- 

 cite. With reference to its age, Emmons says it has been poured out 

 "not only since the deposition of the later Tertiaries [Green River 

 and Vermillion Greek Groups), but since their partial removal by erosion." 

 We have, therefore, in this instance a volcanic rock, the eruption of 

 which must have fallen into a period of time during which a portion of 

 the basalts were ejected. 



In order to present a synopsis of the systematic arrangement of the 

 volcanic eruptives of the Western portion of the United States, I have 

 prepared a table showing their relative positions and giving synonyms 

 as applied to the same rocks in other countries. 



* Bulletin No. 3, American Geogr. Soc. New York, 1877. 

 t Alaska and its Eesources, W. H. Dall., 1870, p. 286. 

 t Geolofjie der Gegenwart, Leipzig, 1872, p. 133. 

 § U. S. Geol. Expl. 40th Parallel, vol. ii, 1877, p. 236. 



