•*** 



6 





y 





a 



•f 



>8* 



Per. 



'ito i 



Uu 



ey 



c 



^ tli 



' h lias 



• a* its 



i state, 



» is to 



ad not 



ace any 



osed to 



com, 



nward, 



ne lava 

 n,tm. 

 a little 



in suck 

 3 moral- 

 ; a heap 

 another 

 ■nihlei 



rv. roll- 

 >ver one 



MM. * 



(5 (the 



ieir eje 





b 



pro 



lop 



on 



i 



a 



e of 



must 

 feff 



literal; 

 rre ^ eI 



Ch. XXV.] 



FLUID LAVA.— ROPY SCORLL 



02 5 



minute, 

 common 



or three-tenths of an inch per second.* ' Although 



lava/ observes Professor Forbes, 'is nearly as liquid as melted 

 •on, when it issues from the orifice of the crater, its fluidity 



more 



rapidly diminishes 

 dened by the consolidated slag through which it has to force 

 its way, its velocity of motion diminishes in an almost incon- 

 ceivable degree ; and at length, when it ceases to present the 

 slightest external trace of fluidity, its movement can only be 



ascertained by careful and repeated observations, just as in 



the case of a 



t 



It appears that the intensity of the light and heat of 

 lava varies considerably at different periods of the 



the 



same 



eruption, as in that of Vesuvius in 1819 and 1820, when Sir 

 H. Davy ^remarked different degrees of vividness in the white 



" -<-—"- ■•■ » lava originated. J 



flame ' and ' smoke ' are used in 

 describing volcanic appearances, they must generally be 

 understood in a figurative sense. We are informed, indeed, 

 by M. Abich, that he distinctly saw, in the eruption of Vesu- 



When 



\ 



flame of burning hydrogen ; & 



flame 



and 



impalpable dust illuminated by that vivid light which is 

 emitted from the crater below, where the lava is said to clow 

 with the splendour of the sun. The clouds of apparent smoke 

 are formed either of aqueous and other vapour, or of finely 

 comminuted scorite. 



Ropy scorice.- In their descriptions of lava, geologists 



sometimes 



umes 



cable. This structure I saw very conspicuously displayed 



from 



N.N 



cone. 



of the crater and descended the .,_._ 0i ^ w tllt; UOIie 



There were no loose fragments of scoria upon it, and the 



^rface had the form partly of ropes and partly of the roots 



trees. Occasionally we may observe such lavas on Etna 



* Phil. Trans. 1846, p. 154. 

 t Ibid. p. H8. 



+ Ibid. 



p. 241 



VOL. i. 



Bulletin de la Soc. Geol. de Franc 

 torn. Tii. p. 43; and Illustration of Ve- 

 suvius and Etna, p. 3. 



S S 



