J. D. Dana — History of the Changes in Kilauea. 223 



small to be elongated much by the flow. This kind of lava 

 occurs in streams outside of Kilauea, and in many about the 

 slopes of Mt. Loa. 



The best example of it I have seen, and the basis of the fol- 

 lowing description, is that of the 1880-'81 Mt. Loa flow, near 

 Hilo. The small uniformly crowded vesicles constitute about 

 40 per cent of the mass. They characterize the lava, with 

 scarcely any change in size and numbers, to a depth (as I found 

 in a tunnel within the lava stream whose floor was similar) of 

 10 or 12 feet. Below this depth of 10 or 12 feet, the lava, as 

 I learned from Rev. E. P. Baker of Hilo, is probably more 

 solid, this being usually the case. 



The scoriaceous kinds are : 



(3) That of the glassy scoriaceous crust of the lava stream 

 inside of Kilauea, and of the scum of its lava-lakes (xxxiv, 354). 

 The vesicles are 65 to 75 per cent of the mass ; they are elon- 

 gated ; those at top mostly closed; those of the bottom of the 

 crust commonly very large. The crust of the lake is sometimes 

 so thin that stones thrown on it slump through. The glass is 

 easily fusible and hence its rapid fusion and cooling. An 

 analysis of this scoria-crust made, at my request, by Professor 

 O. D. Allen, proved it to have the composition of ordinary 

 basalt.* No analysis has been made of the stony lava of 

 Kilauea for comparison. 



(4) Ordinary scoria, such as is common about cinder-cones 

 outside of the crater, mostly stony in texture ; the vesicles 65 

 to 95 per cent of the mass. 



(5) Spongy, thread-lace glass scoria, occurring as a layer 12 

 to 16 inches thick over the southwestern border of Kilauea 

 (xxxiv, 359) ; the vesicles 98 to 99 per cent of the mass ; their 

 walls in the coarser varieties sieve-like or reticulated ; in the 

 finer, like thread-lace in texture. Similar spongy scoria is 

 reported as occurring at the summit of Mt. Loa and about the 

 sources of some of the Mt. Loa lava flows ; but I have seen no 

 specimens. Since a cubic inch of the finer thread-lace scoria con- 

 tains only l'T per cent in bulk of rock material, a layer of solid 



* Professor Allen's analysis (this Journal, III, xviii, 134, 1879) is in column 

 A, below. For comparison, the composition is added of (B) the doleryte (diabase) 

 of West Rock, New Haven, Conn., of Triassic age, by Mr. G. W. Hawes (Ibid., 

 ix, 186, 1875), and of (C) a -'typical" basalt from Buffalo Peak, east of the west 

 fork of the Platte, between the two Parks, by R. W. Woodward (Geol. 40th Par- 

 allel, vol. ii, Descript. Geol., p. 126, 1877). 



Si0 2 A1 2 3 Fe„O s FeO MnO MgO CaO Na 2 K,0 ign. P 2 5 



A 50-75 16-54 2-10 7"88 trace 7'65 11 96 2-13 056 0-35 = 99-92 



B 51-80 14-21 3-55 8'26 0"42 7'63 10-68 2-15 0'39 0-63 0M4 = 99-86 



C 49-04 18-11 2-71 7-70 trace 472 711 4-22 2-11 129 TiO a 2-46 = 99-47 



I add that I do not cite here the analyses of the rocks and volcanic glass of 

 Kilauea made by another for me and published in my Expedition Report, because 

 they are erroneous and should be rejected. 



