46 



Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



section of tlie elevated mass parallel to the general axis of elevation, 

 wiU be bounded above and below by straight horizontal lines. If, how- 

 ever, we now conceive this force to act with greater intensity at particular 

 points along the general line of elevation, the section just mentioned 

 will present such an appearance as represented in the annexed diagram. 



in which the line ABC, previously to the elevation, was horizontal. In 

 such case we shall have longitudinal extension, (equal to the difference 

 between the line ABC and the dotted line AC), which, if sufficiently 

 great, will necessarily produce transverse fissures, similar to the longi- 

 tudinal ones already described, and such as represented in the above 

 section. 



44. We may represent to ourselves this more intense action at 

 particular points, by conceiving an additional force superimposed on a 

 uniform force producing the general elevation independently of the 

 irregularities resulting from this partial action. It is manifest therefore 

 that the tension perpendicular to the line of elevation will result from 

 the sum of these forces, while the longitudinal tension will be produced 

 by the superimposed force alone. The former will therefore, when the 

 partial force is not great, be much the greatest; and we may conse- 

 quently conclude, that the longitudinal fissures may in such case be formed 

 first, during the continuous though rapid increase of intensity in the ele- 

 vatory forces, according to the assumption we have made respecting them, 

 (Art. 12.); and when this system is once formed (the fissures in it not being- 

 remote from each other), the transverse system must necessarily be approxi- 

 mately perpendicular to it, whether it be formed at the next instant, 

 or at any succeeding epoch, and notwithstanding any irregularity in the 

 forces producing it, provided they do not act impulsively. In this 



