E. S. Dana — Petrography of the Sandwich Islands. 461 



structure. It is very light and porous and in each little cavity 

 there are groups of crystals of feldspar in the usual rhombic 

 plates, with minute slender needles of a pale yellow augite 

 iridescent on the surface, and thick tables of titanic iron show- 

 ing large rhombohedral planes (cr=56°). These last have 

 bright faces, often cavernous, and with a bluish steel-like tarnish. 

 The augites are flattened parallel to the orthopinacoid, as 

 shown by the parallel extinction and the oblique optic axis. 

 Chrysolite is present in the mass of the rock but hardly appears 

 in the sections. 



~N~o. 7 is a similar rock, but more compact except for paral- 

 lel lines of cavities partially filled with black glass. No. 6 

 shows the same structure in part, but the mass of the specimen 

 has a base of a very black glass with crystals of feldspar, augite, 

 and broad plates of titanic iron running through it. In the 

 large cavities the crystals of these minerals project out, 

 though the surface of the cavity is lined with a glassy web. 

 One of the sections under examination is cut across the junc- 

 tion and shows both the uniform fine-grained crystalline portion 

 and the glassy part with its large enclosed crystals. A curious 

 feature of the glass is the presence of a swarm of minute apa- 

 tite needles running through it in every direction. These do 

 not extend into the crystallized parts. Apatite usually appears 

 as one of the very earliest secretions from the magma, and why 

 it should be thus localized in these patches of glass while absent 

 from the crystalline parts of the rock, it is difficult to explain. 

 In general, apatite has been found to be a rare constituent of 

 the Hawaiian lavas. 



Two others of the specimens (4, 7) are gray compact rocks 

 extremely fine-grained except for occasional chrysolite grains. 

 N~o. 1 is peculiar in having small uniformly-distributed patches 

 of a dark colored slightly opalescent glass, which is deep brown 

 and nearly opaque in the thin section except as it is penetrated 

 by apatite needles which here also are confined to it. 



With the specimen from Kilauea proper belong those col- 

 lected by Mr. Baker from Nanawale and Makaopuhi, the 

 former chiefly remarkable for their chrysolitic character, the 

 latter sparingly so. Several of the latter specimens are remark- 

 able for that crystalline structure that has been several times re- 

 marked upon, and one of them contains the white zeolitic mineral. 



Former observers have dwelt at length upon the features of 

 the glassy forms of the lava and the presence of glass in the 

 partly crystalline varieties. This is probably to be explained 

 by the fact that the specimens which first present themselves to 

 the collector on his visit to the interior of Kilauea are the 

 superficial more or less scoriaceous or glassy forms which con- 

 stitute merely a crust and do not represent the true character 

 of the average lavas. The writer has found glass only a com- 



