700 DYNAMICAL GEOLOGY. 



3. The wide distribution of volcanoes over the globe affords evi- 

 dence of internal heat. Volcanoes, extinct or active, border the Pa- 

 cific, from Fuegia to Alaska ; through the Aleutian Archipelago to 

 Asia ; down the Asiatic coast, through Kamtchatka, Japan, and the 

 Philippines, to New Guinea, New Hebrides, and New Zealand ; and 

 they constitute half of the islands of this ocean, two of which, in Ha- 

 waii, are nearly 14,000 feet high. This volcanic region is equal to a 

 whole hemisphere, and is therefore evidence of a wide distribution of 

 interior heat. Volcanoes occur also through Java and Sumatra ; in 

 central Asia, in the Thian-Shan Mountains ; about the Mediterranean 

 and Red Seas ; in western Asia, and southern, central, and southwest- 

 ern Europe ; in Iceland, and in the West Indies. 



The ejection of melted rock through fissures has taken place over 

 all the continents : in Nova Scotia, Canada, New England, New Jer- 

 sey, and the States south, the region of Lake Superior, the Rocky 

 Mountains, and western America; in Ireland, Scotland, and various 

 parts of Europe ; and so over much of the globe. 



If all volcanic heat is a consequence of movements in the earth's 

 crust (p. 699), the evidence from volcanoes proves nothing with re- 

 gard to independent subterranean sources. But that this is not so is 

 apparently proved by facts connected with the earth's movements, 

 stated on page 735 ; and consequently igneous eruptions must for the 

 most part have come from great fire-seas, that had their origin in the 

 earth's original liquidity. 



2. EXPANSION AND CONTRACTION. 



1. In Solids: the Heat from an External Source. — The sun is pro- 

 ducing somewhere, at all times, alternations of temperature, and there- 

 by change of size and position ; and the same effect comes from 

 changes of temperature, whatever the source. The cause is universal 

 in its action. 



Colonel Totten, of the United States Engineer Department, having observed that the 

 stones of the coping of a wall became loosened from some cause, undertook, in 1830 to 

 1833, by a series of experiments, to ascertain the effects of the daily and annual change 

 of temperature. He found that an inch of fine-grained granyte (obtained from a bowl- 

 der at the head of Buzzard's Bay) expands, in inches, for an increment of 1° F. 

 •000004825 ; of white granular limestone (from Sing Sing, thirty miles north of New 

 York), -000005668; of red sandstone (from Portland, Conn.), -000009532. These num- 

 bers become, for an increase of 1° F. in 100 feet of the granyte, -00579 in. ; the marble, 

 •00680 in.; the sandstone, -01144 in. ; and for 1° C, respectively, -01042 in., -01224 in., 

 •02059 in. 



Bunker Hill Monument, a hollow obelisk, two hundred and twenty-one feet high and 

 thirty feet square at base (made of granyte blocks), swings to one side and the other, 

 with the progress of the sun during a sunny day — a pendulum suspended from the 

 centre of the top describing an irregular ellipse nearly half an inch in its greatest 

 diameter (Horsford). 



