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



the description of Mr. Brigharn (xxxiv, 95, from page 20 of 

 the same volume) the bottom of the crater had already the 

 form of a low eccentric cone, the surface rising from the foot 

 of the encircling walls to the summit about Halema'uma'u. 

 This has continued to be the form of the bottom, and the 

 Government map gives the present depth. (See the accom- 

 panying Plate I).* 



The following table contains (A) the above deduced figures 

 for the depth of the lower pit ; (B) the height of the highest 

 part of the western wall ; and (C) the level of the center of 

 the pit below the top of the western wall. 



After eruption of 1823 

 1832 

 1840 



Depth of Lower Pit. 



600 (800? ) 

 450 (600? ) 

 385 



Height of W. Wall 

 above ledge. 



900 (?) Maiden 

 715 Douglas 

 650 Wilkes f 



Height of W. Wall 

 above center of 



bottom. 

 1500 (1700?) 

 1165 (1315?) 

 1030 



1868 

 1886 



300 







600 (550?) 



500 Govt. Survey 



900 (850?) 

 380 



These numbers have much instruction in them notwithstand- 

 ing all uncertainties. The following diagram, based on them, 

 represents a transverse section of the crater at the several levels 

 of the floor and black ledge. The minimum depths for 1823 

 and 1832 are here accepted, there being in them no probability 

 of exaggeration. 



1 500 

 .1000 



















ISS3 

 1340 









l X 



— T 







.3500 







1832 







The sides of the pit in this section are made vertical from 

 1823 onward — an error which there are no data for correcting. 



* Mr. Brigham's paper gives results of his barometric measurements iu 1880, 

 that are not reconcilable with those of the Government or of earlier determina- 

 tions except on the assumption of great changes of level between 1880 and 1886 

 and small difference of level as regards the base of the cone between 1840 and 

 1880. His depths are 650 feet at the northern base of the cone near the place of 

 descent, where Wilkes made the depth 650 feet, and the Government map in 

 1886, 481 feet; and 300 at Halema'uma'u, where the Government survey made the 

 depth nowhere less than 320 feet. By the reported measurements, the cone had a 

 height of 350 feet in 1880, and of 150 in 1886; accordingly the base of the cone 

 to the north had been raised 140 feet in the 6 years after 1880 while nothing or 

 little in the 40 years preceding it, although larae overflows during the interval, 

 adding 50 to 100 feet to its height, are mentioned by Mr. Brigham and others; 

 and the level about Halema'uma'u had lost 30 feet between 1880 and 1886. The 

 latter difference of level is not impossible ; but the former it is natural to ques- 

 tion, since so great a rise of the border in 6 years could not have taken place by 

 any method without being noticed. 



f The Wilkes Expedition appears to have made the place of encampment the 

 datum point. The exact position of the place is not precisely known. It may 

 probably be ascertained nearly enough to give by leveling the height with refer- 

 ence to the Volcano House ; but at this time the height has not been determined. 



