448 E. S. Dana — Petrography of the Sandwich Islands. 



The plagioclase feldspar is present in the ordinary forms, and 

 shows no unusual features. The augite forms irregular grains 

 crowded among the feldspars. Occasionally augite in larger 

 more distinctly crystallized forms appears, evidently belonging 

 to an earlier generation. This earlier augite shows the tendency, 

 often observed, to cluster about the chrysolite grains. The 

 titanic iron is not as a rule abundant, and for the most part 

 appears in long slender rods often parallel among themselves 

 over a limited area, and sometimes orientated by the chrysolite. 

 In two or three of the specimens of this class the augite shows 

 a tendency to assume the radiating form but this is the excep- 

 tion. Apatite is probably present in some sections, but only 

 in small amount, and in most cases it was not detected. Glass 

 is almost entirely absent from these rocks. 



The occasional fractured character of the chrysolite has been 

 spoken of; one specimen (90) shows this in an extreme degree, 

 the chrysolite being separated here into many angular frag- 

 ments for the most part showing no crystalline outline. The 

 feldspar and augite individuals have also suffered in the same 

 way and the ground mass has a curiously mottled microcrys- 

 talline structure suggestive of some porphyry. This specimen 

 stands comparatively alone, although two or three others are 

 of somewhat similar character. 



Lavas with minute crystals of feldspar and augite in their 

 cavities. — Allied to this second class of rocks just described, are a 

 number of specimens which are interesting because of their re- 

 markable crystalline structure. One of these (82) is a light gray 

 rock with only occasional vesicles. It is, however, throughout 

 open and porous with minute cavities into which project thin 

 tabular crystals of feldspar seen distinctly with a strong hand- 

 glass. A light yellowish augite is also observed, but the crystals 

 are less distinct. Iridescent grains of chrysolite are scattered 

 through the mass, and the fractured surface shows the same 

 long lines of this mineral that are seen in the sections. 



An interesting feature of this specimen and of others like it 

 (including one very similar collected two or three hundred feet 

 below the summit of the wall making the E.JST.E. side of Ki- 

 lauea, called Waldron's Ledge, also others from Makaopuhi) is 

 the presence in cavities, of a mineral in very minute nearly 

 spherical forms of a milk-white color. These are rather abun- 

 dant through the mass of the rock, each little cavity containing 

 one or two of them. They are so small (rarely more than *2 or 

 .gmm j n di ame ter) that it is very difficult to determine their 

 form, especially as the crystalline faces are dull and give almost 

 no reflections. A hexagonal outline can usually be made out, 

 and occasionally a triangular face through which the angle of 

 another crystal sometimes projects, as if they were complex 

 penetration twins, which the nearly spherical form also sug- 



