270 



DYNAMICAL GEOLOGY. 



extinct. Fig. 228 represents a nearly north-and-south section of the island 

 through Mount Loa and Mount Kea. The slopes of Mount Loa are 5° to 8°, 

 except over its broad nearly flat summit; of Mount Kea, 5° to 10°; and the 

 eastern slopes of Kilauea, only 3°. The map of Hawaii shows also, by the 

 dark-dotted areas, the courses of its great lava-streams since 1840. 



Figs. 229 and 230 are maps, on a scale of 9000 feet to the inch, of the 

 crater at the summit of Mount Loa (Fig. 229) and that of Kilauea (Fig. 230), 

 after an eruption in 1886. 



Fig. 232 is an excellent view of the crater of Kilauea as it appeared in 

 1864, taken from the north side. It differs little from that of recent years, 

 except in the low ridge over the bottom toward its left side. 



232. 



Kilauea, from the north, just west of the Volcano House. Perry. 



233. 



Maui (Fig. 160), the island just northeast of Hawaii, affords, in its east- 

 ern half, another good example of a lava-cone ; its height is 10,032 feet, and 

 the crater, called Haleakala, is 2500 feet deep. 



Cinders, or the material of high projectile discharges, form cinder-cones 

 (Fig. 233), having slopes commonly of 35° to 40°, but made somewhat lower 



after their formation, through the winds, 

 rains, and surface earth-slipping. They 

 have narrow summits and craters. 



If the cinders are wet by heavy rains, or 

 otherwise, so as to flow like mud, the cone 

 formed has a broad top, a saucer-like crater, 

 and slopes generally of 15° to 25°, and is a 

 tufa-cone. The sides may spread out below 

 at a very small angle. Figs. 234 and 235 a,re tufa-cones. They show the 



Aeeumption Island, Northern Ladrones. 

 D. '41. 



