10 DEFINITIONS AND LAWS OF GEOLOGY. 



laneura and Pompeii, and the great eruptions of Vesuvius. In 1669 a current of 

 lava flowed from Etna, having a width of 600 yards, and a depth of 40 feet when it 

 reached the sea at the distance of fifteen miles. In 1783 Skapter Jokul, in Iceland, 

 sent forth two currents of lava in opposite directions, one of which extended fifty 

 miles, and the other forty-five. The extreme breadth of the one in Skapter valley 

 was fifteen miles, and the other had a breadth of seven miles. The ordinary height 

 of the current was 100 feet, but in narrow defiles it sometimes amounted to 600 feet. 

 There is no evidence of a volcanic eruption on the continent of North America in 

 past geological ages that surpassed this in volume. 



About midnight, August 11, 1772, a luminous cloud appeared to envelop 

 Papandayang, a volcano on the island of Java, and in a short time it actually fell in 

 with a great noise. Immense quantities of volcanic substances were thrown out and 

 distributed for many miles around. It is estimated the mountain for fifteen miles in 

 length and six in breadth was swallowed up in the earth by this commotion. Forty 

 villages were ingulfed or destroyed, and 2,957 inhabitants perished. It seems in 

 this instance the eruptions had formed a corresponding cavity beneath the surface, 

 and when the weight above overcame the resistance, the volcano suddenly fell into 

 the abyss beneath. 



A volcano forced its way from beneath the sea into the atmosphere off St. 

 Michael's, Azores, in 1811. It was first seen above the sea on June 13th. The ap- 

 pearances were exceedingly beautiful, the volcano shooting up columns of the blackest 

 cinders to the height of between 700 and 800 feet above the surface of the water. 

 When not ejecting ashes, an immense body of vapor or smoke revolved almost hori- 

 zontally on the sea. The bursts were accompanied by explosions resembling a mixed 

 discharge of cannon and musketry, and a great abundance of lightning. By the 4th 

 of July an island was formed a mile in circumference and 300 feet high. In the 

 center there was a crater full of hot water, which discharged itself through an 

 opening facing St. Michael's. The island subsequently disappeared k beneath the 

 water. 



Twelve islands constitute the Hawaiian Group, four of these are mere barren 

 rocks ; the remaining eight have an area of about 6,000 square miles. All of these 

 islands are volcanic, and no other rocks than volcanic are found upon them save a 

 few remnants of sea-beaches. They are all mountainous, and the deep sea surround- 

 ings have shown the islands are only the summits of gigantic mountain masses. 

 Mauna Kea, on Hawaii, is 13,900 feet above the sea, and Mauna Loa 13,700 feet. If the 

 ocean were driven away, it is said these mountain peaks would stand 30,000 feet above 

 the foot of the mountain range. On Hawaii the volcanic forces are still in opera- 

 tion. On Maui they rested at a recent epoch, or within a few hundred years. On 

 the other islands they have long been extinct, and the piles built up have been 

 greatly eroded. On Hawaii there are two grand foci of volcanic eruption where 

 the fires are now raging, Mauna Loa and Kilauea. Mauna Loa is the largest vol- 

 cano in the world, and none approach it in the magnitude jof its eruptions. A 

 moderate eruption represents more material than Vesuvius has emitted since the 

 days of Pompeii, and the flow of 1855 would have nearly built Vesuvius. On the 

 whole, it appears there are as many active volcanoes, and some as vast and fright- 

 ful in eruptive jpower as seem to have existed at any other single period in geolog- 

 ical time. 



