GEY 



[ 192 ] 



GIL 



six feet in one direction by forty- 

 six in another. In the centre is a 

 pipe seventy-eight feet in perpen- 

 dicular depth, and from eight to 

 ten feet in diameter, but gradually 

 widening as it rises into the basin. 

 The circular basin is sometimes 

 empty, but is usually filled with 

 beautifully transparent water in a 

 state of ebullition. During the 

 rise of the boiling water in the 

 pipe, especially when the ebullition 

 is most violent, and when the 

 water is thrown up in jets, subter- 

 ranean noises are heard, like the 

 distant firing of cannon, and the 

 earth is slightly shaken. The 

 sound then increases, and the 

 motion becomes more violent, till 

 at length a column of water is 

 thrown up, with loud explosions, 

 to the height of one or two hundred 

 feet. After playing for a time like 

 an artificial fountain, and giving 

 off clouds of vapour, the pipe or 

 tube is emptied, and a column of 

 steam rushing up with amazing 

 force and a thundering noise, ter- 

 minates the eruption. If stones 

 are thrown into the crater, they 

 are instantly ejected, and such is 

 the explosive force, that very hard 

 rocks are sometimes shivered by it 

 into small pieces," Lyell. 



Sir George Mackenzie thus de- 

 scribes an eruption of the Great 

 Geyser, " The eruption commenced 

 with a sound resembling the distant 

 discharge of a piece of ordnance ; 

 the sound was repeated irregularly 

 and rapidly, and I had just given 

 the alarm to my companions, (Drs. 

 Bright and Holland) who were at 

 a little distance, when the water, 

 after heaving several times, sud- 

 denly rose in a large column, 

 accompanied by clouds of steam, 

 from the middle of the basin, to 

 the height of ten or twelve feet. 

 The column seemed as if it burst, 

 and sinking down it produced a 

 wave, which caused the water to 



overflow the basin in considerable 

 quantity. After the first propul- 

 sion, the water was thrown up 

 again to the height of about fifteen 

 feet. There was now a succession 

 of jets to the number of eighteen, 

 none of which appeared to exceed 

 fifty feet in height; they lasted 

 about five minutes. Though the 

 wind blew strongly, yet the clouds 

 of vapour were so dense, that after 

 the first two jets I could only see 

 the highest part of the spray, and 

 some of it that was occasionally 

 thrown out sideway. After the 

 last jet, which was the most furious, 

 the water suddenly left the basin, 

 and sunk into the pipe in the 

 centre. The temperature of the 

 water in the basin was ascertained 

 to be 209 Fahrenheit." In a sub- 

 sequent eruption, witnessed by Sir 

 George, there was a succession of 

 magnificent jets, the highest of 

 which was at least ninety feet. 



Dr. Black gives the following 

 analysis of the waters of the geysers 

 of Iceland. Soda 5*56, alumina 

 2*80, silica 3 1 -50, muriate of soda 

 14-42, sulphate of soda 8-57 



The siliceous deposits from the 

 geysers are well known. Sir G. 

 Mackenzie describes the leaves of 

 certain trees converted into stone, 

 every fibre being discernable. 

 Grasses, rushes, and peat are in 

 every state of petrifaction. 



GI'BBOFS. (gilbus, Lat. gilleaux, 

 Fr. gibl6so, It.) Bossed; convex; 

 bunched. In botany, applied to 

 fleshy leaves having one or both 

 sides convex, arising from the great 

 abundance of pulp. 



GI'BBSITE. A mineral of a dirty white 

 colour, found in America, and named 

 after Mr. Gibbs. Its analysis gives 

 alumina 64'8, water 34'7. Specific 

 gravity = 2'4, 



GILL. The lung, or respiratory organ 

 of the fish. The gills, or branchia3, 

 lie in openings on each side of the 

 head; their form is semicircular; 



