March, 1835. volCx^nic phenomena. 



381 



stances. With respect to the cause of the paroxysmal 

 convulsion in particular portions of the great area which 

 is simultaneously alfected, it can be shown to be extremely 

 probable^ that it is owing to the giving way of the superin- 

 cumbent strata, (and this giving way probably is a conse- 

 quence of the tension from the general elevation) and their 

 interjection by fluid rock — one step in the formation of a 

 mountain chain. On this view we are led to conclude, that 

 the unstratified mass forming the axis of any mountain, 

 has been pumped in when in a fluid state, by as many 

 separate strokes as there were earthquakes. For instance^ 

 in the case of Concepcion, during the few months sub- 

 sequent to the great shock, upwards of three hundred 

 tremours of the ground were felt, each of which indicated a 

 fresh fracture, and injection of the fluid stone. It is a case 

 precisely analogous to what happens in all bad eruptions^ 

 which are invariably followed by a succession of smaller 

 ones : the diff*erence is, that in the volcano the lava is 

 ejected, while in the formation of a mountain chain it is 

 injected. This view of the extremely gradual elevation of 

 a line of mountains, will alone explain the difiiculty (which, 

 as far as I am aware, has never been attempted to be solved) 

 of the axis consisting of rock which has become solid under 

 the pressure of the superincumbent strata, while yet these 

 same strata, in their present inclined and vertical positions, 

 cannot possibly cover more than a small portion of that 

 axis. 



