INORGANIC GEOLOGICAL DYNAMICS. 551 



rived great revolutions on the earth's surface, is hypothetical ; and all 

 which depends on this assumption belongs to theoretical geology. 



Confining ourselves, then, to volcanic effects, which have been pro- 

 duced, certainly or probably, since the earth's surface assumed its pre- 

 sent form, -we have still an ample exhibition of powerful causes of 

 change, in the streams of lava and other materials emitted in eruptions ; 

 and still more in the earthquakes which, as men easily satisfied them- 

 selves, are produced by the same causes as the eruptions of volcanic fire. 



Mr. I/yell's work was important in this as in other portions of this 

 subject. He extended the conceptions previously entertained of the 

 effects which such causes may produce, not only by showing how 

 great these operations are historically known to have been, and how 

 constantly they are going on, if we take into our survey the whole 

 surface of the earth ; but still more, by urging the consequences which 

 would follow in a long course of time from the constant repetition of 

 operations in themselves of no extraordinary amount. A lava-stream 

 many miles long and wide, and several yards deep, a subsidence or 

 elevation of a portion of the earth's surface of a few feet, are by no 

 means extraordinary facts. Let these operations, said Mr. Lyell, be 

 repeated thousands of times ; and we have results of the same order 

 with the changes which geology discloses. 



The most mitigated earthquakes have, however, a character of vio- 

 lence. But it has been thought by many philosophers that there is 

 evidence of a change of level of the land in cases where none of these 

 violent operations are going on. The most celebrated of these cases 

 is Sweden ; the whole of the land from Gottenburg to the north of 

 the Gulf of Bothnia has been supposed in the act of rising, slowly 

 and insensibly, from the surrounding waters. The opinion of such a 

 change of level has long been the belief of the inhabitants ; and was 

 maintained by Celsius in the beginning of the eighteenth century. It 

 has since been conceived to be confirmed bv various observations of 



i/ 



marks cut on the face of the rock ; beds of shells, such as now live- 

 in the neighboring seas, raised to a considerable height ; and other 

 indications. Some of these proofs appear doubtful ; but Mr. Lyell 

 after examining the facts upon the spot in 1834, says, "In regard tt. 

 the proposition that the land, in certain parts of Sweden, is gradual!} 

 rising, I have no hesitation in assenting to it, after my visit to the dis- 

 tricts above alluded to." 4 If this conclusion be generally accepted by 



4 Phil. Trans. 1835, p. 32. 



