476 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[vol. 50 



(III) Pumiceous variety < 



Si0 2 95-22 



AI2O3 0.59 



Fe 2 3 . .. • 0.19 



CaO 1.99 



Ign 1 . 20 



Loss at ioo° 0.40 



99-59 



The lime in analysis III was there as a mechanically admixed 

 carbonate. The high ignition (0.99) in II would suggest that a 

 part of the silica is in the condition of opal, as already noted. Elimi- 

 nating the ignition and the free calcium carbonate in III, it is evident 

 that there is no essential chemical difference in the three samples. 

 They vary as little as would probably three independent analyses 

 of any one of the types from slightly different sources. 1 



The distribution about the crater of this altered sandstone is of 

 primary importance. The occurrence of the silica powder (rock- 

 flour) in the dry wash on the south side has been already referred 

 to. Mr. Barringer states that the same material is met with almost 

 anywhere in digging on the outside of the rim, and the shafts and 

 trenches sunk show it to extend to a depth of at least 48 feet, com- 

 mingled with fragments of limestone and sandstone, both unaltered 

 and in the white, pulverulent condition. As described, it has "evi- 

 dently welled out of the crater almost like liquid mud, or, perhaps 

 more accurately, like flour when it is poured out of a barrel"(p. 870). 



The present writer dug fragments of the altered, white, friable 

 sandstone from trenches on the north side, and the same material 

 from the floor of the low place in the north crest of the rim. The 

 finely pumiceous, almost wholly glassy material, the rarest of all, 

 has been found only in shafts sunk from the bottom of the crater, 

 but the coarser material was found in small quantities well out on 

 the lower slopes to the south. The chemical and petrographic work 

 of Messrs. Melville and Diller, elsewhere referred to, was done on 

 material found on the surface and outside of the crater rim. 



The work of boring, as carried on in the interior of the crater, 

 was done with a toothed, hardened steel bit, giving a 2^2 -inch core. 

 Throughout the 500 feet of crushed sandstone a large portion of the 

 material was washed up by a current of water in the form of loose 



'At the time Mr. Gilbert was making his investigations a chemical analysis 

 was made by W. H. Melville of the vesicular variety (No. III). This Mr. 

 Gilbert has placed in my hands. It is as follows : Si0 2 , 89.71 ; Al 2 0s, 1.20 ; 

 FeO, 0.34; CaO, 4.22; MgO, 0.22; K 2 0, 0.15; Na 2 0, 0.24; Co 2 , 3.25; Ign., 

 0.74; loss at ioo°, 0.20; total, 100.27. 



