264 



GROUPS OF VOLCANOES. 



all the day. During the time of this phenomenon, a pungent odour 

 of sulphuretted hydrogen gas was perceived at a great distance, to the 

 surprise of the inhabitants, who did not dare to approach this spot 

 on account of the horrible noises. But many came the following 

 day, and found that the new great orifice, had ejected several streams 

 of liquid chalk {creta), which had covered, with an ashy crust of 

 many feet, all the surrounding space, filling the cavities and chinks. 

 The hard substances ejected were fragments of calcareous tufa, of 

 crystallized gypsum, pebbles of quartz, and iron pyrites, which had 

 lost their lustre, and were broken in pieces. All these substances 

 form the outward circuit at this day. The unpleasant smell of sul- 

 phur still continued, and the water which remained in the holes was 

 hot for many months ; while a keen smell of burning issued from 

 the numerous orifices around the great gulf, which is now completely 

 filled." 



Volcanoes frequendy occur in groups, sometimes arranged along 

 a line, as if they had originally been formed over one vast chasm, 

 like the minor volcanoes on the sides of Etna ; sometimes they are 

 dispersed irregularly over the surface, and sometimes they are isola- 

 ted like Mim, and the Peak of TenerifFe. 



The volcanoes in South America, Humboldt observes, instead of 

 being isolated or disposed in irregular groups as in Europe, are ar- 

 ranged in rows, like the extinct volcanoes of Auvergne, or the vol- 

 canoes of Java ; sometimes in one line, and sometimes in two paral- 

 lel lines. These lines are generally in the same direction, as the- 

 chain of the Cordilleras, but sometimes (as in Mexico) they form an 

 angle with it of 70°. The volcanoes of Mexico, he further ob- 

 serves, are placed in a narrow zone, between latitude 18° 59' and 

 19° 12'. This he regards as a vast chasm, seven hundred and fifty 

 miles in length, extending from the coast of the Adantic to that of 

 the Pacific, and to the islands of Revillagiedo in the same direction. 



Our knowledge of volcanic geography is, at present, imperfect, 

 but among the principal volcanic groups and ranges, the following 

 may be briefly enumerated : — 



In the Azores, there are no less than forty-two active or dormant 

 volcanoes ; and submarine volcanoes, not unfrequently, break forth in 

 their vicinity. Almost all the other islands in the Atlantic, and many 

 of the West India islands, are volcanic. Numerous islands in the 

 Pacific Ocean and the Indian Seas have large volcanoes. In the 

 Island of Java alone, there is a range consisting of thirty-eight large 

 volcanic mountains, some of which are, at present, in an active state ; 

 they are detached from each other, and though some of them are 

 covered by the vegetation of many ages, the indications of their 

 former eruptions are numerous and unequivocal. 



Numerous volcanoes exist, near or within the arctic circle, in ; 

 Kamschatka, in Greenland, and in Iceland. A range of active or | 

 dormant volcanoes extends from the southern extremity of America 



