456 E. S. Dana — Petrogra/phy of the Sandwich Islands. 



were formed by the drying of little bubbles. The augite crys- 

 tals are often rough and black with magnetite. 



Where there are vesicular cavities, often filling the whole 

 interior of the tube, these are lined with a comparatively 

 smooth, shining web of feldspar plates and clusters of brown 

 augite crystals, or of augite needles alone, woven together like 

 basket work. The dull surfaces of magnetite octahedrons are 

 scattered abundantly among the augite and feldspar. The 

 large quantity of magnetite is shown by the fact that the mag- 

 net picks up many of the fragments of the stalactites, even 

 when quite large. The specific gravity of fragments of the 

 solid portion of a stalactite was found to be 2 -98. 



The explanation of the process by which these unique vol- 

 canic icicles have been formed is not easy to give. It is clear 

 that further study, on the spot, of their occurrence and the cir- 

 cumstances of their growth is called for. It seems at first 

 most easy to think of them as made by the rather rapid drip- 

 ping of the semi-viscid lava from the roof. The evidence at 

 hand, however, shows pretty conclusively that they could not 

 have been the result of simple direct fusion. The fact that 

 they hang down, from the solid crust, while the stalagmites 

 formed by the dripping from above rise from tjie solid floor 

 beneath, seems to prove that they were formed after the 

 molten lava had passed by and the temperature had fallen be- 

 low the point of fusion. If made directly from molten mate- 

 rial, they could hardly be so perfectly crystalline throughout 

 as they have been shown to be ; we should expect to find them 

 more like the glassy spatterings from the blow-holes of Kilauea 

 mentioned on a later page. Moreover, the sorting out of the 

 material is further evidence on the same side : the crystalline 

 shell of hematite and magnetite, with its lining of augite, and 

 within the solid crystalline mass, or the clusters of beautiful 

 crystals chiefly of feldspar. Still again, the question has been 

 raised as to whether the flow of a viscid liquid like the mol- 

 ten lava could form drops so small as the size of the stalactites 

 show must have been present. 



The fact that the lava rods or tubes of the stalactites are of 

 nearly uniform size throughout their length, although bunched 

 and knotted together at frequent points as has been described, 

 is an important one.* It separates them, as to mode of origin, 

 from the stalactites of a limestone cavern which form in a 

 more or less conical shape from the flow down over the exterior 

 surface of the lime-bearing solution. It seems to require that 



* A stalactite from a Kilauea cavern collected by Prof. J. D. Dana is of inter- 

 est here, since it forms an exception to those that have been described. About 

 the first formed stalactite, with its rather thick magnetite shell (fig. 11) has been 

 formed a second, somewhat vesicular and nearly concentric with it. This stalac- 

 tite has the exterior coating of gypsum crystals spoken of by Brigham. 



