164 



SCIUJ^CU. 



[Vol. VIII., No. 185 



referred to the pliocene from a study of the abun- 

 dant vertebrate remains found in them. 



In 1871 the writer accompanied Dr. Hayden's 

 expedition of that year from Utah across the Snake 

 Eiver plains, through Idaho to Montana. Old lake- 

 beds were found filling- many of the valleys, — the 

 expansions of all the more important rivers and many 

 of their tributaries having once been lakes. The 

 lacustrine deposits consisted mainly of sands, arena- 

 ceous clays, and what were called ' marls ' They were 

 recognized to be precisely like the beds of the Loup 

 Fork group, generally light colored, white, creamy 

 yellow, or ashy gray, and were referred by Dr. 

 Hayden to the pliocene, from their lithological char- 

 acters. He supposed that the lakes dated back to 

 the pliocene, and that the waters gradually subsided 

 during quaternary times. Specimens of the rocks 

 were collected, in 1871 and 1872, and deposited in 

 the Smithsonian institution. Tbe only fossils obtained 

 in 1871 were a fragment of the jaw of Anchitherium 

 agreste, associated with a helix. Pliocene fossils 

 were found by Dana and Grinnell, in 1874, in a basin 

 on a branch of Smith's Eiver in Montana, but the 

 beds from which they were obtained were only fifty 

 feet in thickness, and differ from the beds of the 

 other lacustrine areas in the mountains. The data 

 as to the age of these supposed pliocene deposits is 

 therefore meagre. Some facts of rather recent dis- 

 covery, however, seem to indicate that possibly their 

 age, and their contemporaneity with the original 

 Loup Fork beds and the jwst pliocene of Hayden, 

 may eventually be established by the study of the 

 lithological characteristics of the various basins. At 

 any rate, certain lines of investigation are suggested 

 that promise interesting results. 



Somewhat more than a year ago Mr. George P. 

 Merrill, of the national museum, informed me that 

 in arranging the ' pliocene marls ' and sands that I 

 had collected in 1871, he was struck with their 

 peculiar appearance ; and upon subjecting them to a 

 microscopic examination, he had found them to be 

 composed mainly of volcanic material, several of 

 them, in fact, being wholly composed of volcanic or 

 pumiceous glass. These specimens were from some 

 of the valleys in the upper branches of the Jefferson 

 Eiver. Although some of the coarser strata of the 

 deposits were recognized in 1871 as being of volcanic 

 origin, that the peculiar ashy gray, drab, and cream- 

 colored beds so characteristic of the lacustrine areas 

 were of a similar origin, was first demonstrated by 

 Mr. Merrill's examinations. This discovery gave 

 additional interest to the study of the Gallatin valley 

 lacustrine area, which has been our field of study for 

 the past two seasons. 



The specimens collected in the summer of 1885 

 have also been examined, and they reveal the fact 

 that the so-called marls and sands are composed 

 largely of pumiceous glass, which was in all proba- 

 bility ejected into the air from volcanic vents, and 

 deposited in the quiet waters of the lake. The char- 

 acter of the beds is such that they are very readily 

 eroded and broken down, which probably accounts 

 for the removal of so enormous a mass from the cen- 

 tral portions of the valley. How great the thickness 

 of the original deposit was, it is impossible to say 

 exactly ; still, the remnants on the south east side of 

 the basin, near Bozeman, represent a thickness of at 

 least eight hundred to a thousand feet. Only the 

 eastern side of the valley has as yet been re-exam- 

 ined, and the beds are so generally concealed along 



the edge of the mountains that it is difficult to obtain 

 a connected section in detail : the general section,, 

 however, has been determined. As in the case of 

 the Loup Fork section, near the mountains, and in 

 the lake basins of other portions of Montana, there' 

 is a progression from calcareous beds up through 

 loosely coherent sands to conglomerates, which cap' 

 the series. Creamy-white limestones with veins of 

 quartz or chalcedony are the lowest rocks of the lake 

 series in the Gallatin valley ; and above them are 

 light yellor.ish-gray, marly-looking sands, distinctly 

 stratified. They are highly calcareous, but, after 

 treatment with hydrochloric acid, the residue is 

 found to be mainly made up of particles of glass. In 

 the central portion of the section near Bozeman, the 

 beds are composed almost purely of pumiceous glass,, 

 while the upper portions show a mingling of particles 

 of crystalline rocks with the glass. The crystalline 

 particles were evidently derived from the mountains 

 near by, when they formed the shore of the lake. 

 The pumiceous particles in the Gallatin valley speci- 

 mens are sharp and angular, and show no evidence 

 of attrition. The conclusion seems inevitable that 

 this material was thrown into the air from some vol- 

 canic vent or vents, perhaps in repeated showers, 

 and deposited in comparatively quiet waters. As 

 the lake became more and more filled up, there 

 appears to have been more agitation in its waters, 

 and particles worn from the shores were mingled with 

 the volcanic materials. That the latter was not 

 carried in by water, seems probable, for the central 

 portions of the beds are almost, if not entirely, made 

 up of glass alone ; and moreover, the finely com- 

 minuted condition of the particles, and. their homo- 

 geneity in close proximity to the shore, confirm the 

 view that they are wind-carried. The general resem- 

 blance of the Montana sections to those of the Loup 

 Fork region led me to look up in the national museum, 

 some of the Loup Fork fossils collected by Dr. Hayden 

 from 1856 to 1857, and described by Dr. Leidy. 

 Sufficient material for microscopic examination was 

 found adhering to many of the bones, and, in nearly 

 every case, pumiceous particles were recognized in 

 the sand. Specimens sent to the writer within the 

 last three months, from several localities in northern 

 and north-western Nebraska, and from north-western- 

 Kansas, have also contained similar volcanic glass. 

 Mr. G. P. Merrill, in the * Proceedings of the national 

 museum for 1885' (p. 99-100), has described volcanic 

 dust from southern Nebraska. Dr. M. E. Wads- 

 worth {Science, vi. p. 63) describes similar material 

 from south-east of the Black Hills in Dakota ; and 

 Prof. J. E. Todd discovered, in 1885, in eastern and 

 north eastern Nebraska, beds of siliceous material,, 

 which were identified by Mr. J. S. Diller as being 

 composed largely of volcanic glass {Science, vii. p. 

 373). We find, therefore, that not only is there a 

 resemblance in appearance and in the order of suc- 

 cession between the Loup Fork beds and the lacus- 

 trine strata of Montana, but that in both, volcanic 

 dust or pumiceous glass enters largely into their com- 

 position ; and it is suggested that future investigations 

 may possibly lead to a determination of their age 

 through the careful study of this volcanic material. 



The fresh-water tertiary formations east of the 

 Eocky Mountains, and even in the mountains, have 

 been supposed to differ from those in the west (in 

 Idaho, Nevada, and Oregon), where the accumulation, 

 of volcanic sediments in the old lake- basins has been 

 recognized by Newberry, King, Eussell, Gilbert, and 



