94 



IGNEOUS AGENCIES. 



time, lava, cinders, ashes, etc., which accumulate immediately about the 

 crater, and continue to increase, by successive layers, with every erup- 



Fig. 77.— Section across Hawaii. 



tion. Ejections of pure lava, particularly if the lava is very fluid, form 

 a cone of broad base and low inclination. This is the case with the 

 Pacific volcanoes. Fig. 77 is a section through Hawaii, showing the 

 slope of the pure lava-cones of Mauna Loa (L), nearly 14,000 feet 



high, and of Mauna Kea (K). Tufa- 

 cones and cinder-cones (Fig. 78) take 

 a much higher angle of slope. 2. 

 With every eruption the powerful 

 internal forces fissure the mountain, 

 in lines radiating from the crater. 

 These fissures are filled with liquid 

 lava, which, on hardening, forms 

 radiating dikes, intersecting the layers of ejections, and binding them 

 into a more solid mass. Fig. 79 shows how these dikes, rendered 



Fig. 78. — Section of Cinder-Cone. 



Fig. 79.— Dikes at the Base of the Serra del Solfizio, Etna. 



