218 Notices respectmg Nexv Books. 



that the destruction of the plain of Siddira was effected by a vol- 

 canic eruption, which caused a subsidenceof the valley of the Jordan, 

 and buried the guilty cities with its ashes. This is a most interest- 

 ing question, and one which theologians and geologists should unite 

 to solve ; but strange to say, the materials for its solution are still 

 very incomplete. Will not one of the many travellers, who annually 

 flock to the Holj^ Land in quest of excitement, make an accurate 

 levelling from the Mediterranean to the Dead Sea, give us a good 

 orographical and geological map of the region round it, or tell us 

 how far the submarine depression extends up the valley of the Jordan, 

 and ^vhethe^ this depressed area is wholly due to subsidence, or has 

 been subsequently extended by aqueous denudation ? 



We cannot attempt to follow Dr. Daubeny through the mass of 

 curious details and philosophic generalizations which he has collected 

 on the volcanos of all countries. We will therefore proceed to the 

 second part of the work, which speaks of earthquakes and thermal 

 springs, as incidental phsenomena supposed to be connected with 

 volcanos. 



In treating of the unquestionable connexion which often subsists 

 between earthquakes and volcanic operations, Dr, Daubeny seems 

 too much disposed, we think, to consider this connexion as universal. 

 Geologists are apt to forget, what would otherwise be a truism, that 

 an earthquake is merely a quaking of the earth ; they seem to infer 

 from the terrific accompaniments of these events, that the earthquake 

 itself is a vera causa, and speak, for instance, of the upheaval of land 

 being due to an earthquake, when in fact the earthquake is due to 

 the upheaval of the land. Now an earthquake ought to be simply 

 defined " a vibratory movement of part of the earth's surface ;" and 

 in ascending towards its cause, we may attribute it immediately to a 

 sudden snapping asunder or rubbing together of two adjacent rocky 

 masses in the focus whence the vibration proceeds. This act of dis- 

 ruption or of friction is the result of internal movements in the body 

 of the earth, and these movements are probably due to a plurality of 

 causes. Volcanic explosions no doubt form one of these causes ; 

 but we wdU not venture to say that they form the chief, far less the 

 only source of these hypogene concussions. Giving volcanic erup- 

 tions full credit for the sudden upheavals of land which they have 

 occasioned, we cannot go the length of attributing to their mechani- 

 cal action the slow and gi-adual elevations and depressions which 

 unquestionably take place. 



These chronic changes of level are much more easily explained by 

 the contraction or expansion caused by a subterranean change of 

 temperature. And this may be due either to a cosmical change in 

 the temperature of the space through which the solar system moves, 

 or to a slow cooling of the earth's interior from radiation, or to su- 

 perficial changes, such as the increase or diminution of ice, or of 

 forests, or of hot or cold marine currents, or to the convection of 

 caloric by thermal springs. It is also, no doubt, often due (as in the 

 Puz/.uoli case) to changes of temperature connected with volcanic 

 agency ; but this is a very different operation from the mechanical 



