462 K S. Dana — Petrography of the Sandwich Islands. 



paratively insignificant element in the normal rocks and often 

 wholly absent, even from those of recent eruption. 



4. Relation between the rocks of the Summit crater of Mauna 

 Loa and those of Kilauea. 



In general, the lavas of the summit crater and of Kilauea, so 

 far as examined by the writer, are strikingly similar in character, 

 all being augitic basalts, varying chiefly as regards the amount 

 of chrysolite present. The clinkstone-like rock of Mokuaweo- 

 weo has not been observed at Kilauea ; but the feathery group- 

 ing of augite and feldspar which characterizes it belongs to the 

 recent Kilauea lavas as well. The darker colored vesicular 

 basalts, which are highly chrysolitic and hence of high specific 

 gravity, are alike from both craters. Writers on volcanoes 

 have attempted to draw conclusions in regard to the distribution 

 of the heavier and lighter lavas according to altitude, limiting 

 the former to the lower levels. This is a natural inference on 

 a priori grounds, but it does not rest on observation as the facts 

 already stated sufficiently show. It is a striking fact in con- 

 nection with the mechanics of volcanic eruptions that lavas of 

 the heaviest character (3 - 15 and 3 f 20) should have been raised 

 to an altitude of nearly 14,000 feet above sea-level. 



The chemical composition* of the Kilauea lavas is well shown 

 by the series of analyses (14 in number,) given by Silvestri, 

 and also those — chiefly of glassy forms — given by Cohen. 



Of these analyses, three by Silvestri, (A, B, C), and two by 

 Cohen (D, E), are quoted here, viz : — 



A. Recent vitreous basalt, fresh and unaltered. 



B. Older basalt, also fresh ; 



C. Older basalt, much altered ; 



D. Compact basalt-obsidian ; 



E. Fele's Hair : 



A. B. C. D. E. 



G. = 2-97 G.-— 3-01 G. = 2-80 G.=2-75 G. = 2'66 



Si0 2 49-20 48-82 4S-60 53-81 50-82 



Ti0 2 1-72 1-16 2-01 undet. 



AI0O3 -- 14-90 15-22 25-45 1348 9'14 



Pe 2 3 -- 4-51 5-72 17-55 3-02 7"33 



PeO 1275 9-65 1-20 7-39 7-03 



MnO 0-28 0-67 tr, tr. 0-38 



CaO 920 10-40 2-20 10-34 11-63 



MgO 3-90 4-55 0'98 6-46 7'22 



Na 2 1-96 2-10 j . „ 3-23 1-02 



KoO 0-95 0-90 } L dB 0-64 3'06 



P 2 5 0-42 tr. tr. 



H 2 0-10 1-87 0-57 1-74 



9989 99-19 99-23 100-95 99-37 



* The remark made by Professor J. D. Dana must be repeated here that the 

 early analyses published in the Geological Report of the U. S. Exploring Expedi- 

 tion, having been made for him by au inexperienced analyst, are entirely unrelia- 

 ble and should Dot be quoted. 



