40 Mr HOPKINS, ON RESEARCHES IN PHYSICAL GEOLOGY. 



parallel fissures may be produced, of which the directions will be per- 

 pendicular to each other. No two systems of parallel fissures could be 

 thus formed, of which the directions should not be perpendicular to 

 each other. (Art. 32.) 



X. If the fissures in either of these systems be near to each other, 

 they could not be formed by such tensions as we have been considering, 

 in successioti. They must be formed simultaneously in each system. One 

 system, however, might be formed at any time subsequently to the other. 

 (Art. 30, 32.) 



