48 Dana — Observations of F. 8. Dodge on Halema?uma?u. 



Figure 4. — Cross-seciion of Colby Mine through both north and south ore-depos- 

 its. The perpendicular line running through the figure is drawn because the 

 two parts of the section are not exactly upon the same plane. They differ 

 from this so slightly, however, that the true relations of the ore-bodies to the 

 surrounding rocks are shown by the combined figure. Scale 1" = 210'. 



Figure 5. — Elevation of Pence Mine, looking north. The eastern pitch of the 

 dyke is again observable. The right-angled trough made by the dyke-rock 

 and quartzite is in this case not filled with ore throughout the whole figure. 

 At the eastern end of the figure after passing through a heavy bed of drift, 

 the ore constitutes the rock surface. Scale 1"=210'. 



Figures 6, 7 and 8. — Cross-sections of same at No. 1, 2 and Father Hennepin 

 shafts respectively. In figure 8, the shaft has not yet passed through the 

 ore. Scale 1"=210'. 



Figure 9. — Section designed to show the variation from unaltered carbonate to 

 ferruginous chert and ore-bodies in passing from higher to lower horizons, 

 and to illustrate the manner of ore-concentration: S=Upper Slate, Q=Quartz- 

 ite, FQ = Feldspathic Quartz-slate. Scale 1"=1230'. 



Figures 2 to 8 inclusive are from surveys made and blue-prints furnished by 

 Messrs. J. Parke Channing and C. M. Boss, of Bessemer, Mich. 



Art.' IV. — Recent Observations of Mr. Frank S. Dodge, 

 of the Hawaiian Government Survey, on Halema? uma? u 

 and its debris-cone / by James D. Dana. 



Mr. Frank S. Dodge has recently made a new survey of 

 Halema'uma'u, the great South Lake basin of Kilauea, which 

 gives definite facts as to the gradual lifting of the debris-cone 

 of the basin, and sustains his conclusions from previous obser- 

 vations that the cone has been floated upward on the column 

 of lavas beneath the floor of the basin. 



The accompanying map and the sections 2 to 5, reduced 

 from copy recently received by the writer from him, present 

 the chief results of his survey. In addition I have from him 

 a brief letter of explanations. The scale of the map is 2000 

 feet to the inch, which makes the distance across the basin from 

 east to west (New Lake not included) a little over 3000 feet. 

 The outline of the debris-cone at base is approximately indi- 

 cated by the dotted line. The numbers give the level, below 

 the Volcano House datum, of three points at the top of the 

 cone as well as of the floor of the basin and of the crater out- 

 side. At m, n, o,p. q, r are small discharging cones, ten to 

 twenty feet high. Two of these small cones, m and n, were at 

 such a height, owing to the rising of the floor of the basin, 

 that their lava streams overflowed the rim of the basin ; and 

 from o, the lavas had flowed into New Lake. 



Figures 2 to 5 are four profile sections by Mr. Dodge, AB, 

 CD, EF, GH, of the basin and its cone. The height in these 

 sections is exaggerated five times, but in fig. 2, the profile a b 

 has the true proportions. In 2 and 3, jp is the pit within the 



