﻿of Montana and Idaho. 



201 



in the accompanying figures (fig. 2) from Mr. Eidge way's draw- 

 ing. I can think of nothing with which they compare in 

 appearance more nearly than that of lunar landscapes, as illus- 

 trated in works on popular astronomy. 



The second variety from this locality (358936) is a fine- 

 grained, compact, dark brownish gray rock, bearing little 

 resemblance to the others de- 2 . 



scribed. It is not at all friable 

 but effervesces readily with acid. 

 Fragments after treatment with 

 acid till they no longer give off 

 bubbles fall readily to a powder, 

 which the microscope shows to 

 consist almost wholly of quite 

 large pumice fragments, some- 

 times colorless but often stained 

 a bright yellow by ferruginous 

 matter. A few crystalline par- 

 ticles are present but so stained 

 as to be unrecognizable. The 

 glass in this sample shows no trace of the peculiar disc-like 

 bodies noted on the last. 



Marsh Creek Valley, Idaho. — Of the four samples from this 

 locality the first two (35889a) like 35890a from Little Sage 

 Creek, are nearly pure pumice dust, but the particles have 

 suffered more from attrition, and are so filled with minute 

 cavities as to have a dirty appearance under the microscope. 

 The rock is ash-gray and has a sharp gritty feel. 



The second (358896) is much firmer in texture, laminated, 

 slightly coarser and contains black particles. Its composition 

 is, however, practically the same with the addition of a little 

 calcite whicn" serves as a cement. The rock effervesces readily 

 under dilute acid, and the residue is all glass with no crystal- 

 line particles whatever. 



The fourth specimen (35889c), although coarser and of a 

 brownish color, is also largely pumice dust, but the particles 

 are quite dirty-appearing under a low power, an appearance 

 which a power of 420 diameters shows to be due to their rough, 

 almost granular surfaces. There is but little calcite present. 



Port Neuf Carton. — The two specimens (35892) from this 

 locality compare closely macroscopically with the finer varieties 

 from Little Sage Creek and Marsh Creek Yalley. Like them 

 too they are composed wholly of minute fragments of pumice 



(fig- S). 



These last, like some of the others mentioned, contain evi- 

 dently two kinds of pumice dust. The one occurs in colorless 

 shreds with curved outlines, which rarely contain tubes or steam 



