E. 8. Dana — Petrography of the Sandwich Islands. 449 



gests. Only one of these forms was detected in the thin sections, 

 and the free side of this had a hexagonal outline, the whole 

 being divided into sectors which alternately had like extinc- 

 tion, the surface of the sector being mottled in polarized light 

 after the manner of some crystals showing anomalous optical 

 double refraction. The fact that these little white spheres 

 occur also on the inner glazed surface of the vesicles would 

 seem to mark them of subsequent origin and hence probably 

 zeolitic. Their form suggests a rhombohedral zeolite grouped 

 like phacolite or the Australian herschelite. Two or three 

 other zeolitic minerals were observed in isolated cases, but too 

 sparingly and in too minute form to be satisfactorily identified. 



In other specimens of this class (as 105, 107) the color is 

 darkened because of slight alteration, the texture is coarser and 

 the cavities larger. Here the clear glassy feldspar tablets are 

 very distinct, and augite crystals, red or brown on the surface 

 and opaque, also project into the cavities. Octahedrons of 

 magnetite are often seen implanted upon the augite needles, 

 and broad plates of titanic iron, with rhombohedral planes on 

 the edges, sometimes attain a relatively large size. The feld- 

 spar tablets were here large enough to allow of their being 

 separated and examined optically. In form they are either 

 rhombic or acute triangular in outline, being bounded by the 

 planes c (001) and y (501) or c and x (101), with the prisms very 

 small when present at all. They can often be seen to be twins 

 in accordance with the usual albite law. The extinction on the 

 clinopinacoid made an angle of — 14 to — 15° with the basal edge, 

 which conforms to typical labradorite, as might have been antici- 

 pated. These highly crystalline specimens are also much like 

 some of those collected from ejected masses about Kilauea, and 

 they may here have had a similar origin. 



All the specimens that have been thus far described were 

 obtained with a single exception (No. 74 already located) either 

 from the talus in the southern crater against the wall of the 

 neck that joins it with the central pit, or else from the east 

 side of the interior of central Mokuaweoweo. Nothing can be 

 said in regard to the relations in place of the two types of 

 basalt which have been described and which occur together at 

 the points mentioned. 



Other varieties of the lavas. — A number of the specimens 

 cannot be classed in either of these two groups. They are light 

 gray in color, not vesicular, and sparingly provided with chryso- 

 lite, if it is present at all, and characterized by a very uni- 

 form granular mixture of augite and plagioclase. A specimen 

 taken from a vein in the western wall belongs here, also another 

 stated to have come from the highest point on the edge of the 

 crater. Still another specimen from the north brink is similar, 

 but is porphyritic with patches of a glassy plagioclase. 



