Volcanoes. 153 of lava and basalt, are covered with loose stones, scoria, and ashes. A record of the eruptions of Hecla has been chronicled since the loth century, and they number 43. One of its most violent convulsions occurred in the same year as that of the ‘ Skaptar-Jokull,’ viz., in 1783. At a distance of two miles from the crater, the lava flood was one mile wide, and 40 feet deep, whilst its fine dust was scattered as far as the Orkney Islands, 400 miles distant. The mountain itself is composed of sand, grit, and ashes, several kinds of pumice stone being thrown out of it. It also ejects a quantity of a species of black jaspars, which look as if they had been burned at the extremities, while in form they resemble trees and branches. All the different kinds of lava found in volcanoes are to be met with here, such as agate, pumice stone, and both black and green lapis obsidian. These lavas are not all found near the place of eruption, but at some dis- tance, and on their becoming cold form arches and caverns, the crust of which being hard rock. The smaller of the caverns are now used by the Ice- landers for sheltering their cattle. The largest of the caves known is 5034 feet long and from 50 to 54 feet broad and from 34 to 36 feet high. It is believed by some geologists that a subter- ranean channel connects the volcanic vent of Hecla with the great central one of Askja. This theory is based on the fact that a number of lava floods have burst forth simultaneously at different times

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