E. S. Dana — Petrography of the Sandwich Islands. 445 



Occasionally the feldspar is present in larger forms ; and 

 more interesting to note is an occasional augite crystal (fig. 1, h) 

 that evidently belongs to an earlier generation, and shows the 

 distinct cleavage, and more or less also the cr} ? stalline outline of 

 the species. The alteration to which this specimen, with others 

 like it, has been subjected, and to which the red or purple color 

 of the rock in the mass is due, has stained the iron red and 

 reddened also the augite, although only exceptionally to such 

 an extent as to make it opaque. The alteration spoken of may 

 be simple weathering, although the occasional brick-red color 

 rather suggests the action of hot water or steam ; the feldspar 

 remains perfectly clear and unchanged. 



From the specimen described, which may be taken as the 

 type, we pass to the coarser grained kinds on the one hand and 

 to the very fine-grained on the other ; both of these still retain- 

 ing, however, the same general characters. A highly cellular 

 specimen (74) with large vesicles, from the northwest brink of 

 the crater, departs in general aspect most widely from the type ; 

 but, while relatively coarse-grained, it exhibits the same group- 

 ing though somewhat more rigid and geometrical, and shows 

 even more clearly the mutual relations of the feldspar and augite. 

 In the finer grained varieties (as 78) the augite sometimes pre- 

 dominates so largely that the whole becomes like a confused 

 carpet pattern of interlacing arabesque forms, though here, 

 when an individual form can be traced out, it has great beauty 

 and perfection, branching and re-branching like some delicate 

 forms of vegetation. Figure 1, g is an attempt to illustrate one 

 of these forms, but it lacks the delicacy of the original. These 

 forms consist almost exclusively of augite with very little feld- 

 spar. In another specimen of similar character a partial fluidal 

 structure was noticed in the arrangement of the feldspar. 



When the iron grains are only sparingly present and there 

 has been no conspicuous alteration, the rock is of a light uniform 

 gray, but the presence of iron in large amount makes it nearly 

 black and obscures this structure ; and when it and the augite 

 are highly altered, the rock is a bright brick-red and in a 

 section appears as a collection of nearly opaque red rosettes, 

 the feldspar, however, still remaining clear. Glass is present 

 occasionally, but usually in insignificant amounts, and for the 

 most part it is nearly or quite absent. This feather-form of 

 augite, which has been described, is not entirely confined to the 

 clinkstone-like varieties of lava although eminently character- 

 istic of them. It was occasionally noted more or less distinctly, 

 in some other forms, especially the vesicular kinds to be men- 

 tioned later (p. 450) where it is seen in the minute second- 

 generation augite which formed in the last process of consoli- 

 dation. All the facts observed serve to connect its formation 

 with rapid cooling. 



