278 Notice of Active and Extinct Volcanos. 



the same time the current of water that continued to flow in. In 

 this manner the water might be propelled in jerks, as happens 

 in the case of the Geyser springs. 



" Such an explanation however is far from being adequate to 

 account for the complicated phenomena of these fountains, which, 

 after a pause of many hours, first threw up water, and after- 

 wards vast columns of steam, to the height sometimes of two 

 hundred feet, and then immediately sunk into a temporary re- 

 pose ; neither is it applicable to the singular circumstance men- 

 tioned by Mr. Henderson, as to the possibility of bringing on the 

 explosion at any given time by merely throwing large stones into 

 the orifice. The latter fact indeed seems to prove that the gen- 

 eration of steam is constant, and that nature has provided other 

 vents sufficient to carry off a certain portion of the elastic va- 

 pour, unless when obstructed in the manner produced by Mr. 

 Henderson, in which case its rapid accumulation gives rise to an 

 almost immediate explosion." 



The celebrated surturbrand of Iceland is spoken of as being 

 almost the only substance in that country not connected with 

 volcanic operations, for almost the whole island is the work of 

 volcanic fire. 



" The west side of a perpendicular cleft in the side of a moun- 

 tain called Hagafiall exposes a section of ten or twelve horizon- 

 tal strata, of Avhich the surturbrand is undermost, occupying four 

 layers, which are separated from each other by intermediate 

 beds, of soft sandstone and clay. 



" They vary in thickness from a foot and a half to three feet, 

 and differ also in quality, the two lowest strata exhibiting the 

 most perfect specimens of mineralized wood, free from all foreign 

 admixture and of a jet black, the numerous knots, roots, &c. leav- 

 ing no doubt of its vegetable origin. The two upper strata con- 

 tain an admixture of earthy and ferruginous matters, and in the 

 midst of them occurs a thin layer, four inches in thickness, con- 

 sisting of a schistose mass which appears to be made up entirely 

 of leaves closely pressed together, separated only by a little 

 clay. These leaves are chiefly of poplar, a tree, Mr. Hender- 

 son says, at present not met with on the island. The beds of 

 surturbrand support an alternation of basalt, tuff, and lava, which 

 extend to the summit of the hill. 



" With the sole exception perhaps of this substance, the whole 

 of the mineral structure of Iceland may be said to have origina- 

 ted more or less directly from volcanos, and there is probably no 

 part of the globe in which operations of this kind have been 

 going on with so much activity, and for so considerable a period. 



