OF THE APPALACHIAN CHAIN. 519 



phenomena, especially by the uniformity in the direction which 

 the earthquake takes, and by the opening of great chasms and 

 fissures in the ground, parallel to each other, and perpendicular 

 to the course of the shock or undulation. Thus it is recorded, 

 that, during the earthquake that shook the valley of the Mississippi, 

 in 1811, the inhabitants felt the earth rise in great undulations, 

 and that the ground opened in numerous parallel fissures, having 

 a direction from northeast to southwest. This close correspond- 

 ence between the direction of the cracks, and that which invariably 

 characterizes our Appalachian axes or faults, is a remarkable 

 circumstance, that well demands the attention of geologists. It 

 lends a further probability to our hypothesis, which merely imag- 

 ines a very much more energetic series of undulations to have 

 occurred during the elevation of all this part of the continent. 

 There is reason to think that this agreement in the direction of 

 the forces at periods so remote, is not merely casual ; for it appears, 

 from a statement of Michell, that of five considerable earthquakes, 

 felt in New England before his time, three are known to have 

 come from the northwest, and the other two are supposed to have 

 had the same direction. Recent observations in Scotland indicate 

 that the earthquake which was there felt in October, 1839, con- 

 sisted of undulations moving from northwest to southeast, or in 

 a direction perpendicular to the strike of all the older axes of that 

 country. 



Of the manner in which the wave-like movements in earth- 

 quakes may be supposed to originate, JVIichell suggests, that large 

 tracts of country may rest on fluid lava, which, when ■ disturbed, 

 may transmit its motion through the overlying crust ; but he offers 

 the following as the explanation of the mode in which the undu- 

 lations may take place. " Suppose a large cloth, or a carpet, 

 spread upon a floor, to be raised at one edge, and then suddenly 

 brought down again to the floor ; the air under it being by this 

 means propelled, will pass along, till it escapes at the opposite 

 side, raising the cloth in a wave all the way as it goes. In like 

 manner, a large quantity of vapor may be conceived to raise the 

 earth in a wave, as it passes along between the strata, which it 

 may easily separate in a horizontal direction, there being litfle or 



