280 SIR RODERICK I. MURCHISON'S ADDRESS. [May 23, 1859. 



of Dr. Volger are faitlifal, and that tliey will afford materials for 

 the elucidation of the phenomena of earthquakes, I must say, as a geo- 

 logist, that I differ from his views, and adhere to the prevalent belief 

 that the chief cause of all earthquakes is the effort of heat and gas to 

 burst through the cerements composing the crust of the earth. I do 

 so, because I every where trace the most intimate relations between 

 earthquakes and volcanicity, both in those tracts where that force is 

 at present in action, and in those where it has formerly shown 

 signs of emission through fissures in the older rocks. On the other 

 hand, the large regions like Eussia in Europe which, as I have else- 

 where shown,* have never been affected by eruptive rocks (or in 

 other words where the crust of sedimentary matter has never been 

 broken through in ancient periods), are just those countries in 

 which earthquakes have been and are unknown. 



All those great movements of the earth's crust which have been 

 so instrumental in producing and modifying from time to time the 

 geographical features of our planet belong, I conceive, to the same 

 class of phenomena as ordinary earthquakes, and are to be referred 

 to similar causes acting with different degrees of intensity. Every 

 great movement must, in fact, have been attended, towards the 

 boundaries of the regions to which it extended, by those smaller 

 movements, reduced for the most part to vibrations, to which the 

 term earthquake has been usually restricted. Hence the theory of 

 earthquakes can only be regarded as a subordinate part of any more 

 general theory which may deal with all those movements, great or 

 small, to which the superficial portion of the globe has been sub- 

 jected, and which constitute, in fact, the basis of geological science. 

 The smaller movements are those alone which man has had 

 actual opportunities of observing, and hence the investigations of the 

 phenomena attending them, and the causes to which they are assign- 

 able, have been separated from those of the allied phenomena some- 

 what more perhaps than some geologists might think desirable, and 

 have been erected into a separate branch of science, under the 

 name of Seismology. Dr. Young and Gay Lussac had suggested that 

 earthquake shocks were propagated in a way analogous to the 

 vibrations of sonorous bodies, but no attempt had been made to 

 unite into a whole the mass of heterogeneous and other apparently 

 conflicting facts, and account for them by the application of one 

 consistent theory. 



In February, 1846, Mr. Eobert Mallet read to the Eoyal Irish 



* See * Russia in Europe and the Ural Mountains,' chapters first and last. 



