J. D. Dana — Metamorphism from Volcanic Conditions. 109 



mountain or leaving very apparent traces in the walls. The 

 summit crater, as described by visitors, has, like Kilauea, walls 

 made of the edges of lava streams, without intercalations of 

 prominent beds of scoria or other fragmental material. 



II. Metamokphism an Effect of Volcanic Conditions. 



The projected rocks of the region about Kilauea are a promi- 

 nent source of evidence as to metamorphism by means of vol- 

 canic heat — as remarked on page 289 of volume xxxv ; and 

 other facts of like import are derived from the lava-stream 

 tunnels and caverns. The rocks referred to, and those also of 

 the lavas generally, as well as the cave products, will be 

 described by Mr. Dana in a following part of this volume. 

 I briefly mention here a few of the facts that have a special 

 bearing on metamorjDhism. 



1. The minute crystals in the cavities of the ejected masses, 

 instead of being zeolites, such as exposure to the weather might 

 have produced, have been proved by Mr. Dana, as has been 

 stated to be identical with the anhydrous constituents of the 

 lava. Minute transparent acicular crystals have given him 

 the angles of pyroxene ; white rhombic tables, the characters 

 of a triclinic feldspar, so that they are probably labradorite ; 

 and besides, there are brilliant iron black octahedrons of mag- 

 netite and tables of hematite or titanic iron. These are all 

 the constituents of the basalt except the less constant one, 

 chrysolite. 



2. The caves and tunnels of Kilauea and of the Mt. Loa 

 lava- stream of 1880-81, afford stony stalactites, remarkable for 

 their slender pipe-stem like size and form, scarcely tapering at 

 all except at the extremity, where there is usually a short 

 irregular twist. The diameter is hardly a fourth of an inch. 

 In 1840 I found only short specimens in the caves of Kilauea : 

 but in 1887 in the tunnel of the lava of 1880-81, near Hilo, 

 many were 20 to 30 inches long ; and in some undisturbed 

 parts of the tunnel there were thickets of these, long gray- 

 black stalactites, one every six or eight inches. Over the floor 

 beneath each, there is a column of stalagmite of similar nature, 

 which is a heap of bent coalescing drops or anastomosing stems 

 from a few inches to fifteen or more in height. Most of the 

 stalactites were solid, with occasional cavities, but many were 

 tubular. Mr. Brigham observed them in the Kilauea caves in 

 1864-5, and has good figures on page 463 of his Memoir. 



These stony stalactites appeared, under a pocket lens, to be 

 identical with the rock of the lava-stream, even to the laths of 

 labradorite, and the cavities showed minute transparent acicu- 



