Mb HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



47 



manner ,t is easy to understand the formation of a transverse system 

 of fissures approximating to the law of parallelism, though resulting 

 from forces which, acting partially, and under other circumstances, would 

 produce the most irregular phenomena. 



45 If however this more intense action at particular points be suf- 

 ficiently great, and exactly simultaneous with that of the general elevatorv 

 force ,t may modify materiaUy the position of the longitudinal fissures. 

 To determine the nature of this modification, we must consider the 

 directions of the tensions which would be produced by an elevatorv 

 force, acting solely in the vicinity of any proposed point of a mass- 

 because such tensions superimposed upon those produced by a force 

 acting uniformly along the whole range, will be very nearly equivalent 

 to the tensions produced by the simultaneous action of two forces such 

 as those just mentioned. 



46. For the greater simplicity, we may take a cone as the ap- 

 proximate type of the partial elevation we have to consider. 



Let A'C'B' represent this cone, CB its axis. Then if we assume 

 the physical hne A'pC to be equally extended, and AD to be its 

 original length, we have 



The original length of A'p : ^> ;: AD : AC, 

 and therefore. 



The original length of A'p = A'p ^^ 



'■ AC 



= A'm, 



