90 J. D. Dana — History of the Changes in Kilauea. 



as Mr. Brigham reports, " with the main wall of Kilauea " 

 "marking the limits of Dana's black ledge " [that is the black 

 ledge of 1840] ; " composed of fragments of all sizes and 

 shapes, very solid and heavy, and full of small grains of olivine." 



A recent letter from Mr. Brigham informs the writer that the 

 ridge ij (which is not particularly mentioned in the report) had 

 the same constitution as ef, but consisted of larger blocks. 



Other interesting features, indicated on the map are (1) a wall, 

 a b, — fault- wall — enclosing an amphitheatre, that of the Hale- 

 ma'uma'u region, perhaps a result of a discharge at some unre- 

 corded time of the lavas of the lake ; (2) just north of this, a 

 deep fissure c d, concentric with the wall a b; and (3) warm 

 or hot steaming caverns in the floor of the crater, some of 

 which were hung with gray-black, often tubular stalactites."* 



The text states that in 1864 the " black ledge " region was 

 fifty feet below the level of the interior plain of the crater, and 

 that the difference in level was the same in May, 1866, although 

 both had been much raised, " at least a hundred feet," the 

 former by overflows and the latter without overflows.* 



Mr. Brigham does not allude to Mr. Lyman's explanation of 

 the long ridge of lava-blocks. He remarks as follows on p. 

 421, after stating the constitution of the ridge, as already cited: 

 " This wall, which is concentric with the main wall of Kilauea, 

 is said to rise and fall and sometimes disappear, which seems to 

 be a fact* although no one has ever seen it in motion. It is 

 the fragments broken from the edge of the crater by an eruption 

 and floated out to its present position." Again, p. 415, " From 

 a manuscript map prepared by Mr. Lyman, I find the ridge 

 occupied the same position as at present." Again, in his ac- 

 count of the crater in May, 1866, p. 427 : " The ledge of broken 

 lava which swept around the eastern end of the crater, marking 

 the limits of Dana's black ledge, is nearly covered with the 

 successive overflows." 



The Great Lake had a diameter of about 800 feet in 1864, 

 and of 1000 in August, 1865. Its lavas in 1864 were 50 feet 

 below the edge, and extended into caverns beneath it. The 

 action was mostly feeble, "occasionally a crack opened and 

 violent ebullition commenced at several points; again it was 

 liquid, but soon passed to the viscid condition ; again " boil- 

 ing violently and dashing against the sides, throwing the red- 

 hot spray high over the banks." There were two small islands 

 in the lake in 1864; but in August, 1865, they had disappeared, 

 and the lavas were then only 30 feet below the edge. 



*The composition of the material of the stalactites, as given in the text. p. 463, 

 from au analysis by Mr. John C. Jackson, is: Silica 51-9, alumina 13"4, iron sesqui- 

 oxide 15-5, MnO 0-8, lime 9 6, magnesia 4-8, soda 30, potash 1-1 = 100. Specific 

 gravity 2-9. The temperature of the caves was usually 80°-95° F. 



