﻿of Montana and Idaho. 



203 



A second variety (38447) from the south side of Bridger 

 Creek, on summit of hill near Bozeman, is like the last but 

 somewhat coarser, and contains also a few colorless polarizing 

 fragments and particles of hornblende. A variety (38450) from 

 the " upper beds," south side of 3. 



the creek, is of a brown-gray 

 color like that of Dry Creek. It 

 is composed almost wholly of 

 very pumiceous glass like fig. 

 3. Still a fourth sample (38449), 

 from a bed just below the last 

 is gray in color and much coarser, 

 the fragments being in some cases 



m 



greatest diameter. It 



0-74 1 



contains also a few polarizing 

 grains. 



Small particles of pumice glass 

 were also found in connection 

 with sundry fossil bones from the Niobrara, Loup Fork and 

 Sweetwater regions. These bones had been quite thoroughly 

 cleansed and handled over many times so that very little of the 

 material in which they had originally been imbedded remained. 

 Nevertheless by carefully picking between the teeth, in cavities 

 and protected places, sufficient material was obtained for micro- 

 scopic examination which resulted as noted. 



"While working upon the above, several other instances of 

 the occurrence of this dust came to my notice which perhaps 

 may be of sufficient interest to mention here. One of them 

 sent by a friend in Phoenix, Arizona, is of a white and gray 

 color sufficiently compacted to be cut in blocks of considerable 

 size, and is stated to have been used to some extent for build- 

 ing purposes. It is stated to occur in " blankets " from three 

 to fifteen feet thick, more or less tilted, and cropping out near 

 the base of the Mazatzol Mountains at the edge of Verde Eiver 

 valley. The microscope shows this to be composed of pumice 

 fragments of about 025 mm greatest diameter, and apparently 

 identical with that described by myself from Southwestern 

 Nebraska* (see fig. 35), and quite similar to that from east of 

 the Black Hills, Dakota, described by Dr. Wadsworth in Science 

 of July 24, 1885, a sample of which he has been kind enough 

 to send me. 



About this same time Mr. R. T. Hill, of the Geological 

 Survey, brought me a sample of similar dust which he had 

 collected from near Wray Station (B. & L. R. R.) in Eastern 

 Colorado, on the south side of the Republican River (38430), 

 and a few days later others were brought in by Dr. Peale 



* Proc. Nat. Mus., vol. viii, p. 99. 



