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



described ; and these graduate into broken scoriaceous lava- 

 flows. 



In two of the aa streams near Punaluu the lava is but slightly 

 chrysolitic; in a third somewhat more recent stream, situated 

 not a mile farther west, the lava is very abundantly chrysolitic. 

 All the facts appear to show that there is no connection be- 

 tween kind of rock and kind of flow. 



16. The enormous bomb-like masses of some aa streams. — The 

 bombs, as they might be called, of the aa streams are, inside and 

 out, in striking contrast with the other masses. Many of them 

 occur in the Kapapala stream, and also in those near Punaluu. 

 They are smoothish exteriorly, more or less rounded and bowl- 

 der-like ; and they vary in size from a mean diameter of a few 

 inches to ten feet and more. One of them is represented in the 

 aa picture at the top to the right (p. 362). 



Some of these bombs consist outside of a crust, four to six 

 inches thick, of hard grayish, slightly vesicular basalt, and inside 

 of fragments of reddish or grayish scoria, the shell being packed 

 full of the scoria fragments. In others similar, the scoria was 

 partly rolled up. Some of them consisted of concentric shells, 

 hard and scoriaceous shells alternating with one another. One 

 had a nucleus of scoria 18 inches in diameter ; and around 

 this, successively, a stoney shell of 3 inches ; a scoriaceous 

 layer of 1 to 2 inches ; a stoney shell of 4 to 5 inches, and 

 then, outside, a rough lava shell 6 inches thick. One of 

 large size, broken open on one side, had had its inside filling of 

 scoria worked out by the natives, and so made into a small 

 cave. 



A common size is three to five feet in diameter : but one 

 enormous bomb, in the aa field west of Punaluu, measured 

 24x12x9 feet in its extreme dimensions, and contained at 

 east 1,000 cubic feet. Enough of its hard outer shell was 

 pealed off to ascertain that the second layer was much vesicu- 

 lar or scoriaceous, and the next layer inside, hard basalt again. 



These bombs lie in the midst of the other blocks of the aa 

 stream, proving that all had a common origin, and that they are 

 not projected bombs, and hence, properly, not bombs at all.* 



The further discussion of the phenomena of Kilauea is left 

 for the " Summary and Conclusions." 



[To be continued.] 



* The word a-a is pronounced as if written ah-ah, the vowels in all Hawaiian 

 words having the Italian sounds ; au has the sound of ow in English. Kilauea 

 has an accent on the e, and Haleakala on the a before the k. Pahoehoe means 

 smooth and shining, and its use is not confined to lava. 



