OF THE HAWAIIAN ISLANDS. 



453 



I have therefore placed first, the fresh lavas which reach the atmosphere in a liquid 

 condition, a class varying in each crater, and even in consecutive eruptions of the same 

 crater; next, the lavas acted upon by gases while still heated; lavas more or less decom- 

 posed by aqueous and acid vapors ; lavas acted upon by the atmospheric agents simply ; and 

 finally lavas which reach the air through water, by which they are more or less comminuted 

 and decomposed, forming tufas. 



As the Hawaiian lavas are extremely liquid, the component parts have every opportunity 

 for free motion, and from this perhaps results the homogeneity of most of the ejected 

 matter. With the exception of chrysolite and augite no minerals have been found in the 

 lavas which have not been formed, in all probability, since the matrix has cooled. 



Native Sulphur. 



This mineral is found principally on the outer walls of Kilauea, and over the fumaroles 

 in Puna which are in close connection with this crater. As the sulphur is first deposited 

 in the crust of the decomposed lava, near the surface, it is usually in fine almost acicular 

 crystals of great beauty. The heat varies from time to time, and the crystalline deposits are 

 often melted by the high temperature (220° Fahr. observed), and form on cooling thin and 

 irregular layers or veins which show an almost prismatic structure, breaking readily in 

 planes at right angles to the surface of the layers. The color is usually pale lemon yellow, 

 but occasionally the presence of selenium is indicated by a deep orange color. The crystals 

 are seldom perfect, being usually formed of concentric coatings with cavernous faces. A re- 

 markable specimen is represented in the figure of the actual size. It 

 was found in Pima and drawn on the spot ; it was so exceedingly 

 brittle that it broke in fragments on removing it from the slab of 

 lava under which it formed. The opposite ends of the vertical axis 

 are not symmetrical, and while the successive layers commence at 

 the upper pole and terminate abruptly at equal intervals as they ap- 

 proach the diagonal axes, the layers on the lower half of the crystal 

 commence on the plane of the diagonal axes, and terminate as on 

 the upper half, but in reversed order. This was by no means an 

 unique specimen, many similar ones were observed. 



The whole amount of sulphur on the Hawaiian Islands is small, and it will perhaps never 

 become an article of commerce, but the deposits are generally quite pure and easily reached. 

 The absence of this mineral, so commonly considered a necessary concomitant of volcanoes, 

 on the other islands, with the exception of the few traces on Haleakala, arises perhaps from 

 the fact that sea-water does not intercept or commingle with the sulphurous fumes. The 

 Sicilian deposits were probably due to the presence of the sea above the lower parts of 

 Trinacria where the sulphur is mostly found. So in Spain, and at Husavik and Krisuvik 

 in Iceland, and at the sulphur-beds of Japan. 



Pyrites. 



This is not found in any recent lava, but apparently arising from decomposition of the 



silicates containing a large proportion of ferruginous oxides, by aqueous action ; as the 



globular or reniform nodules, the most common form, are usually found in wet places where 



the ancient lava has long been exposed to the water. So comparatively rare is this mineral, 



Sulphur Crystals. 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. Pt. 3. 



115 



