OF THE HAWAIIAN ISLANDS. 455 



the hotter fissures sulphurous acid was abundant. 1 Humboldt saw, from the summit of Pich- 

 incha, that at a considerable depth in the crater blue flames moved about, and he distinctly 

 recognized the smell of sulphurous acid. 2 The sulphur banks of Kilauea have a temperature 

 of 210° Fahr. just beneath the outer crust, while at a depth of several inches, near the 

 steam cracks, the temperature rises as high as 220° Fahr. 



This gas combining with hydrosulphuric acid, which is found in the cooler portions of the 

 crater, especially when largely diluted with aqueous vapor, is decomposed, and furnishes the 

 deposits of sulphur in the sulphur banks. Over the more intensely heated Halemaumau 

 the hydrosulphuric acid is consumed on reaching the atmosphere, and this seems to be the 

 source of most of the aqueous vapor in the cloud which overhangs the crater. The steam 

 is in very small quantities, for the smoke is remarkably dry and consists almost wholly of 

 sulphurous acid. 



Sulphuric Acid. 



In crevices in the sulphur banks small quantities of dilute sulphuric acid were observed, 

 probably the result of the decomposition of hydrosulphuric acid. Many years ago Breislak 

 observed that unless this gas was considerably heated when coming in contact with the 

 atmosphere, no sulphur was deposited, but sulphuric acid was formed. 3 



Carbonic Acid. 



Nowhere in the crater is carbonic acid evolved ; and I have not seen proofs of its ex- 

 istence in a free state anywhere about the Hawaiian volcanoes. It is by no means a usual 

 concomitant of volcanoes, and seems limited to those which, like Vesuvius, penetrate lime- 

 stone strata of a former age. 



jSassoZiu — Boracic Acid. 



This was observed in minute quantities in only one fumarole, although looked for with 

 care. It encrusted the decomposing lava, and was much mixed mechanically with sulphate 

 of lime and with silica. 



Quartz. 



Fine crystals have been found in cavities of ancient blue basalt at Onomea, Hawaii, which 

 were from half an inch to an inch in length, quite symmetrical and without modifications, 

 usually attached by the basal pyramid to the basaltic matrix. The cavities in which they 

 were found were generally smooth within. Milky quartz is quite common on Molokai and 

 other islands, and occurs in irregular rounded masses, from one to eight inches in diameter; 

 it is often colored superficially by oxide of iron. Chalcedony is found in botryoidal masses, 

 and mamillary concretions, often of considerable beauty, on Kauai, and has been formed by 

 the solution of the silica in the lava by the soda, set free, perhaps, by atmospheric agency; 

 and this soluble silicate of soda is again decomposed, depositing the silica in thin layers. 

 The silica, separated from the basalt in the sulphur banks, forms a cement for the aluminous 

 earths with which it seems mechanically united, and so far as I have observed, is not separated 

 in these places in distinct masses. The quartz crystals found at Onomea were undoubtedly 

 formed after the lava cooled, as they were found within spherical cavities attached to one 

 side, with perfectly sharp angles. The stratum of blue basalt was about twenty feet thick, 



1 Annales de Chhn. et de Phyx , t. Hi. p. 5. 'i Bischof, C/iem. Geol., vol. i. p. 330. 



2 Ibid., t. xxvii. p. 129. 



