BRITISH ASSOCIATION. 



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cially; and the strata may often be supported in their 

 new position by subterranean injections not visible on the 

 surface. 



Identity of tlie Undulations which 'produced the Axes, with 

 the loave-like motion of the Earth in Earthquakes. — The 

 authors suppose all earthquakes to consist in oscillations of 

 the earth's crust propagated with extreme rapidity; and 

 they ascribe this movement to a sudden change of vertical 

 pressure on the surface of an interior fluid mass, throwing 

 it into wave-like undulations, such as would produce per- 

 manent flexures in the strata if more energetic, accompanied 

 by the formation of dykes. The successive earthquakes of 

 any region usually proceed from the same quarter, and this 

 must also have been the case with the movements which 

 gave rise to the parallelism of contiguous anticlinal lines. 

 In illustration of the power of producing permanent lines of 

 elevation which earthquakes have exhibited in modern times, 

 the authors instance the UUah Bund, an elevated mound 

 extending 50 miles across the eastern arm of the Indus, 

 which was the result of the great earthquake of Cutch in 

 1819; and another case recorded in ^ Darwin's Journal of 

 Travels in South America,' which a traveller described as a 

 line of elevation of the strata, crossing a small rivulet, and 

 shown in the fact that he found himself going down hill, 

 while ascending the dry deserted channel. 



Bate of the Appalachian Axes, — The authors describe the 

 elevation of this chain as simultaneous with the termination 

 of the carboniferous deposits of the United States, and as 

 the cause which probably arrested the further progress of 

 the coal formation. With one local exception, on the Hud- 

 son, the whole series seem to have been deposited conform- 

 ably, without any emergence of the land. That the ele- 

 vation did not take place later, is shown by the undisturbed 

 condition of the overlying beds, approximately of the age of 



