LAV 



some ancient lava, full of subter- 

 raneous caverns, penetrated and 

 melted down part of it. On the 

 18th of June, another ejection of 

 liquid lava rushed from the volcano, 

 which flowed down with amazing 

 velocity over the surface of the first 

 stream. After flowing for several 

 days, it was precipitated down a 

 tremendous cataract called Stapa- 

 foss, where it filled a profound 

 abyss, which that great waterfall 

 had been hollowing out for ages, 

 and again the fiery current pursued 

 its onward course. On the 3rd of 

 August, fresh floods of lava still 

 pouring from the volcano, a new 

 branch was sent off in a different 

 direction. "When the fiery lake 

 which filled up the lower portion 

 of the valley of the Skapta had 

 been augmented with new supplies, 

 the lava flowed up the course of 

 the river to the foot of the hills 

 whence the Skapta takes its rise. 

 This eruption did not entirely cease 

 till the end of two years, and al- 

 though the population of Iceland 

 did not exceed fifty thousand, not 

 fewer than twenty villages were 

 overwhelmed, besides those inun- 

 dated by water, and more than 

 nine thousand human beings per- 

 ished, together with an immense 

 number of cattle. Of the two 

 branches of liquid lava, which 

 flowed in nearly opposite directions, 

 the greater was fifty, and the lesser 

 forty miles in length. The extreme 

 breadth which the Skapta branch 

 attained in the low countries was 

 from twelve to fifteen miles, that 

 of the other about seven. The 

 ordinary height of both currents 

 was one hundred feet, but in nar- 

 row defiles it sometimes amounted 

 to six hundred." The sources 

 from which lava ascends are deeply 

 seated beneath the granite ; but it 

 is not yet decided whether the 

 immediate cause of an eruption be 

 the access of water to local accu- 



[ 250 ] L A U 



mulations of the metalloid bases of 

 the earth and alkalies ; or whether 

 lava be derived directly from that 

 general mass of incandescent ele- 

 ments, which may probably exist 

 at a depth of about one hundred 

 miles beneath the surface of our 

 planet. Lyell. 



LATJ'MONITE. Diatomous zeolite. Lo- 

 monit of "Werner : Mesotype Lau- 

 monite of Brongniart : Zeolite eff- 

 lorescente of Brochant : Diatomous 

 Kouphone Spar of Mobs. A miner- 

 al long known under the name of 

 efflorescent zeolite, and to which 

 its present name has been assigned 

 by Werner, in honour of M. Gillet 

 de Laumont, to whom we are in- 

 debted for our first knowledge of it. 

 It is of a white, or grayish- white 

 colour, sometimes tinged with red. 

 It occurs regularly crystallized, and 

 in distinct granular concretions. 

 Its crystals are four- sided prisms, 

 slightly oblique, sometimes termi- 

 nated by dihedral summits, some- 

 times truncated on their lateral 

 edges. The height of the prism is 

 to the edges of the terminal faces, 

 in the ratio of eight to seven. This 

 prism divides in a direction parallel 

 to all its planes, but much more 

 easily longitudinally than on its 

 terminal surfaces ; this division 

 takes place also with greater faci- 

 lity on two of the opposite sides 

 than on the two others. "When 

 Laumonite has not been altered by 

 exposure to the atmosphere, it cuts 

 glass easily. By exposure to the 

 air, Laumonite disintegrates, and 

 is at length reduced to a white 

 powder. If, however, recent spe- 

 cimens be immersed for two or 

 three hours in a strong mucilage of 

 gum, the action of the atmosphere 

 upon them, and their efflorescence, 

 will be prevented. By the action 

 of acids, Laumonite is reduced to a 

 state of jelly. Under the blow-pipe 

 it fuses, with a slight degree of 

 ebullition, and affords a perfectly 



