THE CRUST OF THE EARTH. 



that the escape of the lava through it is intercepted. In 

 such cases the pressure of the fluid matter acting against the 

 walls of the cleft, or channel, breaks through them at one or 

 more points of least resistance, and new issues are formed on 

 another side of the original crater. These lateral craters may 

 also be produced, even though the central crater is still in activity 

 (% 57). 



137. Volcanic eruptions are not confined to the land, but are 

 often produced in the bed of the ocean. In such cases islands 

 often rise suddenly out of the bottom of the deep. Thus, in 

 1831, the island of Julia arose in the Mediterranean, about 30 

 miles to the south-west of Sicily. Bogoslaw appeared in like 

 manner, in 1814, in the Aleutinian Archipelago ; Sabrina and 

 another among the Azores, in 1811 ; besides various others around 

 Iceland, in the Indian Archipelago, the Philippines, the Moluccas, 

 and off the coast of Kamtschatka. One of the most remarkable 

 examples of these was presented in the case of the island which 

 rose above the waters, in 1796, at 30 miles from the northern 

 point of Unalaska, one of the Aleutinian islands. A column of 

 smoke was first seen to rise out of the sea. This was followed by 



the appearance of a black point at the 

 surface of the water, from the summit 

 of which blades of flame and incandes- 

 cent matter were launched with violence. 

 These phenomena continued for several 

 months, during which the island in- 

 creased greatly in magnitude and height. 

 Afterwards, smoke alone issued from 

 it, which, after continuing four years, 

 ceased. The island nevertheless, still 

 continued to increase in magnitude and height, without manifest- 

 ing volcanic phenomena. In 1806, it had so augmented that 

 it formed a cone, which could be perceived from Unalaska, upon 

 which were formed four other smaller cones in the north-west side. 



138. Some remarkable examples of submarine eruptions have 

 been presented from the most remote times, in the Mediterranean 

 and the Levant. According to ancient historians, the bay included 

 between the islands of Santorin and Theresia (fig. 58), in the 

 Grecian Archipelago, has been the special theatre of these 

 phenomena. The island of Santorin is a half-moon-shaped tract 

 of land, evidently of volcanic origin, and the islands of Theresia 

 and Aspronisi, extending between the horns of the crescent, 

 enclose the bay. Within this enclosure, the island of Hiera rose 

 above the water in 186 B.C., and round it, and close to its coast 

 several islets appeared in 19 A.D., 726 A.D., and 1427 A.D. In 



104 



