AND THE WEST INDIAN ERUPTIONS OF 1902. 



211 



not necessarily a mountain or a liill, although the accumulation 

 of the ejectamenta around the vent forms elevations of greater 

 or less altitude and magnitude. Where, however, no accumu- 

 lation takes place, as when from extreme violence the ejected 

 material is widely dispersed, then a depression rather than an 

 elevation is the result. 



Leaving out of account such minor action as that of 

 fumaroles, solfataras, salses, etc., volcanic eruptions may be 

 roundly regarded as of three kinds : (1) emissive eruptions ; 

 (2) explosive eruptions; (3) partly emissive and partly 

 explosive eruptions. 



The first of these, emissive eruptions, is perhaps best 

 exemplified by the lava flows of Mauna-Loa in the Sandwich 

 Islands. From the two craters of this very extensive 

 mountain mass, one, the summit crater, 13,675 feet, and the 

 other, the crater of Kilauea, 4,000 feet above the level of the 

 sea, a very fluid lava occasionally flows, and spreading out, 

 forms successive sheets of basalt with a very gentle inclination, 

 only from about 4° to 4-75^, and not separated by beds of scoria? 

 or ash. 



In the prehistoric volcanic district of Auvergne in central 

 France, there are domes of trachyte formed by acidic lavas 

 without craters, which have evidently been the result of 

 the cooling of a very viscid lava that has solidified without 

 flowing away from the vent, which has thereby been sealed 

 over with solid rock. 



Lava flows in such cases of purely emissive eruptions are 

 miaccompanied by noise or violence, and are merely, as it 

 were, springs of fluid rock-matter rising from the deep 

 interior through conduits to the surface, the lava being of 

 dift'erent degrees of fluidity according to its varying chemical 

 composition. The lava of Kilauea, being very basic, has 

 indeed such great fluidity that it is drawn out into capillary 

 glass by the wind, and this is called " Pele's hair," from the 

 same goddess that has given the name to the Martinique 

 volcano. 



The explosive eruptions give the most terrific of all volcanic 

 outbursts, although they are sometimes on quite a small scale. 



In these eruptions no lava is seen, but instead there is an 

 ejection, either continuously for a short time, or intermittently, 

 of fragmentary material, with explosive violence, and thundering 

 noises both in short detonations and continuous roars, and 

 accompanied with subterranean rumblings and earth tremors 

 and movements. 



