400 W. T. BRIGHAM ON THE VOLCANIC PHENOMENA 



tially the same material, the results of examinations of both these forms may be placed 

 side by side. 



Al s 3 Fe O Fe 2 3 Mn 2 Ca O Mg O Na KO HO 



13.0 15.0 7.8 8.9 0.4 4.5 2.3 = 100.9 C. T. Jackson. 1 



7.8 13.7 13.0 8.4 5.1 1.8 trace 0.5 = 99.5 J. C. Jackson. 



30.26 18.16 = 99.61 B. Silliman, Jr. 



10.55 22.29 2.74 2.40 21.62 .33 = 99.67 " " 



6.16 28.72 7.40 2.00 6.00 = 100.28 J. Peabody. 



33.62 3.06 1.13 10.52 = 99.60 B. Silliman, Jr. 



14.07 16.91 6.20 1.73 6.31 = 97.15 " « 



I. Lava drops. Color dark bottle-green ; very frangible, like unannealed glass. Sp. gr. 2.7 ; from Halemaumau. 

 II. Pele's hair from Kilauea in 1864; both protoxide and peroxide of iron were present, but owing to the presence 

 of oxide of manganese the proportions could not be determined. III. Pele's hair from Kilauea in 1840 (United 

 States Exploring Expedition). IV. Pele's hair, ditto. V. Pele's hair light colored, ditto. VI. Vitreous lava from 

 Kilauea; Sp. gr. 2.91. VII. Scoria from Kilauea 1840 ; Sp. gr. 2.505. Of the last five the solubilities in hydro- 

 chloric acid were as follaws : — 



Soluble in hydrochloric acid. Insoluble. 



IH. 49.51 50.49 



IV 48.80 51.20 



V. 



VI 42.50 57.50 



Vn. . . . 45.84 54.16 



The fresh crust from the surface overflow of the pools often looks quite firm on 



Crust. . 



the surface, while within it presents a series of small cells surrounding larger, all 

 with the walls of a brilliant metallic lustre. Its composition closely approaches that of 

 Pele's hair. The lava that breaks out of the cones in Kilauea is less porous than this scum, 

 but is still quite cellular. It is viscid, and where it runs over light scoria? does not sink into 

 the porous mass, but flows above, bending slightly, where unsupported, between the frag- 

 ments. Often a fractured surface is brilliantly iridescent. The bubbles or air-cells are 

 generally, but not always, elongated in the direction of the flow. Usually the fresh lava 

 exhibits chrysolite in exceedingly small particles, and so red as to mislead at first in regard 

 to its true nature. Where a large quantity of lava escapes at once, the cooled crust is quite 

 distinct from the cellular portion under it, and is quite compact, vitreous, and easily separable 

 from the rest of the mass. As the small streams cool almost equally above and below, the 

 melted matter solidifies in a cylindrical form which twists if one side cools faster than 

 the other, and produces the rope-like masses so common on the outskirts of lava flows. If 

 the supply is very abundant, the cooling goes on principally at the upper surface, and broad 

 sheets of a sort of pahoehoe are formed. What is most curious, while the general mass of 

 a lava flow — I am now speaking of the comparatively insignificant flows from the pools in 

 the crater — is of a tolerably compact stony nature, a thin layer of very cellular lava 

 separates it from the compact vitreous crust. It is so often declared that the surface of 

 lava is porous and spongy from the escaping gases, that I have been surprised to find that 

 this is not the case. The surface, although covered with glassy scales, perfectly flat and by 

 no means bubbles, is more impervious to gases than is the lower stony mass. The lava as 

 it flows out is not in an effervescent state ; it is simply melted, not boiling rock, and evidently 



1 This, and other analyses, were kindly made for me by Dr. C. T. Jackson and his son Mr. J. C. Jackson. 



