Products of Eruption. 



27 



larger fragments of rock or with fragments of coral reef and shells as in the case of 

 Diamond Head, which exploded through the reef (Fig. 20), forming a coarser con- 

 glomerate. The varying color, brown to red, comes from the decomposition of the 

 hydrous ferrous oxide (Fe^Oj-j-Aq. ). The coarser black sand (Fig. 24) is formed by 

 the forcible contact of molten lava with water, as at Nanawale when the lava stream 

 of 1840 fell into the sea. 



Scoria, a term originall}- applied to the slag or dross of metals, has been rather 

 loosely applied to all the odds and ends of a lava discharge, from a-a to cinders. The 



BASALTIC PRISMS IN WAILUKll GORGE. 



finer scoriae or cinders are the constituents of cinder cones like those on Mauna Kea, 

 which hold together chieflj' by the cohesion of the rough surface of the cinders. The 

 black sand ( Fig. 24 ) is found in la3-ers under Honolulu and elsewhere, and is much 

 used in building operations. — 



The vapors or gases emitted from the craters of the volcanoes when active are 

 never true smoke, but mainly steam. In the crater of Kilauea a distinction must be 

 made between the vapors from Halemaumau and those arising from the outer crater: 

 the latter being the rain products either directly, as after a shower, or from the more 

 lasting surface springs. It is remarkable how permanent some of the steam-holes 



around Kilauea are. I have observed some of the more prominent ones, as those near 



[405] 



