DEFINITIONS AND LAWS OF GEOLOGY. 11 



§ 15. An earthquake in New Zealand in 1856 raised a tract of land compris- 

 ing 4,600 square miles, from one to nine feet. In 1822, and again in 1835, the coast 

 of Chili for several hundred miles was elevated from one to three or four feet or 

 more. The estimated area raised in 1822 amounted to 100,000 square miles. In 

 1819 an earthquake at Cutch, in the delta of the Indus, raised an extent of country 

 about fifty miles long and sixteen miles wide, ten feet, while a considerable tract in 

 the delta of the Indus sank down. Such are a few of the effects produced by earth- 

 quakes in the present century ; they are similar to those which have occurred in 

 every century during the historical period, and are quite as extensive as any we 

 are warranted in believing occurred in any of the earlier geological ages. 



§ 16. It is said large tracts of land are elevated and depressed without the in- 

 tervention of earthquakes. It is said there has been an elevation of land bordering 

 the Baltic, during the historic period, of about three feet in a century. The whole 

 coast of Scandinavia is said to be gradually rising at a very slow pace. A large 

 area in Greenland is reported as slowly subsiding. At Fort Lawrence, in the Bay 

 of Fundy, there is a pine and beach forest covered at high tide by about thirty 

 feet of water. And it is claimed there is some evidence of subsidence on part of 

 the New England Coast, where we have the most indubitable evidence of an eleva- 

 tion of several hundred feet since the beginning of the Post-pliocene period, but these 

 elevations and depressions may have been accompanied with earthquakes. 



§ 17. Earthquakes and volcanoes have a common origin, the former always 

 accompany the eruption of the latter, and it is not likely any great areas of land 

 rise or fall without the intervention of the same energies. The proximate cause of 

 volcanic and earthquake phenomena is not fully known, and it is much easier to 

 show the improbability of the many theories offered for their explanation than to 

 present one free from objections. Volcanoes are intermittent in their eruptions ; 

 they act by spasms of activity, separated by intervals of repose. If they were vents 

 to internal fluidity of the earth, the streams of flowing fire would be constant, not 

 intermittent explosions. If they were vents to any great mass of melted matter pent 

 up until strength enough were obtained to force a passage way to the surface of the 

 earth, when the vents would open the reservoirs would exhaust themselves and close 

 forever. Volcanoes are not to be attributed to the remains or residue of enormous 

 heat contained in the globe, at some remote period of its physical evolution, or con- 

 sidered as lending any support to the nebular hypothesis, or the theory that the 

 earth was at one time in a gaseous or fluid condition. 



Geyser (from the Icelandic word geysa, to gush,) is a periodically eruptive or 

 intermittent hot spring, from which the water is projected in a fountain-like column. 

 The analogy between it and a volcano is so striking that it might be called a volcano 

 erupting hot water instead of melted lava. In the case of a geyser, cold water is 

 supposed to sink from the surface to heated rocks; it starts as a passive liquid, 

 and by its molecular absorption of heat is converted in the depths into an elastic, ex- 

 plosive gas, which ejects it through another orifice to the surface. The gas forces 

 out the column of water and escapes ; then quiet ensues until a new supply of water 

 is furnished. This accounts for the intermitting flows. Grant the local heated con- 

 dition of the rocks below, and all the phenomena of the geysers may be ac- 

 counted for. 



The melted lavas of volcanoes bring up with them great quantities of the vapor 



