MAGMATIC DIFFERENTIATION IN HAWAII 303 



Column 2 gives the average composition of four typical lherzo- 

 lites. 1 In spite of any uncertainties as to the exact compositions 

 of the femic minerals, it is clear that the nodule is, chemically, a 

 lherzolite. 



The writer believes that these nodules are not exotic, but rep- 

 resent segregations in their respective magmas just as truly as do 

 the olivine phenocrysts. Easy transitions in size are to be found, 

 in the field, between large, single phenocrysts of olivine and the 

 largest olivine nodules observed. 



Notes on other lava flows, studied microscopically. — On the trail 

 from the Volcano House to Mauna Kea, at about the 6,000-foot 

 contour (see Fig. 1), the flow of 1880-81 was found to be olivine 

 basalt of the pahoehoe type. The adjacent flow of 1855 is similarly 

 composed but has local aa phases. Still farther north the trail 

 crosses the " ancient flow " shown on the government map (marked 

 "ancient" in Fig. 1); this is an olivine basalt with typical aa 

 habit. At the wagon-road between Waimea and Kailua, the great 

 flow of 1859 is an olivine-poor to olivine-free basalt with both aa 

 and pahoehoe phases. 



Projected blocks at Kilauea and Hualalai. — E. S. Dana has 

 already described the common, basaltic types of rock represented 

 in the solid projectiles thrown out in the rare explosions which 

 have occurred at Kilauea. 2 The present writer has made a micro- 

 scopic examination of seven different specimens of the projectiles 

 sampled at intervals along the edge of the Kilauean sink from 

 Uwekahuna to Kilauea Iki. All of them are holocrystalline and 

 they are non- vesicular or else nearly free from pores. In the 

 coarser blocks the pores are true miaroles, into which the feldspar 

 and augite, showing crystal facets, have grown. The rock species 

 included in this small collection are: basalt poor in olivine; typi- 

 cal olivine diabase; olivine-free diabase; and a typical, relatively 

 coarse-grained olivine-free gabbro. 



Of these, the gabbro is the only type worthy of special remark. 

 It composes several of the projectiles occurring on the road from 

 the Volcano House to Kilauea Iki, near Waldron's Ledge. The 



1 See Proc. Amer. Acad. Arts and Sciences, XLV (1910), 226. 



2 See J. D. Dana, Characteristics of Volcanoes (New York, 1891), 344. 



