HEAT — VOLCANOES. 697 



(No. 2, fig. 974) ; after three days it was continued by means of a second out- 

 break, 4000 feet lower, or 10,000 above the sea, which also was a quiet one. At 

 this second opening, as described by T. Coan, there was a fountain of fiery 

 lavas, 1000 feet broad, playing to a height at times of 700 feet, with indescri- 

 bable grandeur and brilliancy. There were rumbling and muttering from the 

 plunging flood, and explosions, but no earthquakes. Mr. Coan attributed the 

 fountain to the hydrostatic pressure of the column of lava above. 



In August, 1855, another great eruption began (No. 3, fig. 974), without 

 noise or shakings, at an elevation of 12,000 feet, and for a year and a half the 

 flood continued : the whole length of the stream was sixty miles. 



In January, 1859, there was still another eruption (No. 4, fig. 974). It made 

 its first appearance near the summit, in the same quiet manner as the preceding, 

 Ivilauea remaining undisturbed. About 1500 feet above the sea, on the north- 

 west side of the mountain, there was a larger opening, where the lavas were 

 thrown up, "like the waters of a geyser," to a great height. The stream 

 here became wider, subdivided into three or more lines, and continued on 

 towards the base of Mount Hualalai; from this point it bent northward, and 

 then northwestward again, and finally entered the sea on the western coast, 

 after a course of over fifty miles. 



There were thus three great eruptions from the summit, with intervals of only 

 three years and a half, and four within sixteen years. 



In the eruptions of Kilauea — one of the largest of volcanic craters — there 

 is evidence only of the action of hydrostatic pressure and of vapors quietly 

 evolved, as the causes of the outbreak. The fountain had a head of lavas 

 3000 to 4000 feet high,- and 3000 feet of lavas correspond to 3750 pounds of 

 pressure to the square inch. In the eruptions from the summit-crater of Mount 

 Loa the fountain-head is 10,000 to 13,000 feet above the sea; and the eruptions 

 were hardly less exclusively a result of hydrostatic pressure. 



In the eruptions of Vesuvius, there are usually earthquakes of more or less 

 power, lofty ejections of cinders and dark vapors, a breaking of the mountain's 

 summit on one side or the other, or fissures opened in the sides below. In these 

 violent ejections there may be proof of a sudden evolution of vapors. But 

 pressure also acts as at Mount Loa; for the volcano, during the year or niore 

 preceding, has become charged nearly to its brim, ready for the outbreak. 



(c.) Eruptions mostly through Jissures. — Most eruptions take place 

 through fissures in the sides of the mountain, and not by overflows 

 of the craters. The fissures may come to the surface only at inter- 

 vals, so as to appear like an interrupted series of rents, although 

 continuous deep below ; and they may underlie the erupted lavas 

 as far as the flow extends, although nothing appears to indicate it, 

 owing to their being concealed from view by the lavas. But fre- 

 quently small cones form over the wider parts of the rent, and 

 stand along the lava-field, marking the courses of the fissures. 



This method of eruption through fissures makes dikes (p. 122) 

 in the mountain ; and all volcanic mountains, when the interior 

 is exposed by gorges, contain dikes in great numbers. After the 



